Ive been there, done that. But its a learning expierence. So everytime I remove an axle, I 'take note of the position, and number.' as park tool says

And how many times have you guys installed a knobby tire backwards? toooooo many

mmmhmmm

I once didn't engage enough threads with my crank puller and destroyed the threads on the crank arm when I tried removing the crank arm. I ended up having to file down the bottom bracket shoulder to remove it, along with the attached crank arm, with vice grips.

coomer, when u gonna put your new build up?

the first one wasnt my own error but the mechanic's at the bike shop i took my s**** to.

i got a new wheel that came with a ****ty cog and lockring, but i wanted to use my old ones because they were much better quality. i didnt have a lockring tool at the time so i tried to pop the lockring off with a hammer and a flathead screwdriver. that was kinda dumb, so i took both wheels to the mechanic and said, here, switch these cogs out for me. so he takes it and says ok. and i go browse the shop for maybe five minutes, and i come back and he is standing there at the counter struggling with something. i go over and hes trying to get the lockring off. turning it the wrong way. and i come up to him and ask him if hes sure he knows what hes doing, and he looks at it for a second, and then says oh yeah, its the other way isnt it?
at that point i was just like ok, im not taking my eyes off this idiot. 4 minutes later, he comes over to me. excuse me sir but it seems that ive stripped your cog. and not the ****ty aluminum one either. the 50 dollar bank buster cog i bought because it was the only one available at the time that i had learned to appreciate. if anything he should have replaced it free of charge. nope.
needless to say i was just a bit ticked off.

and then one time i replaced the stem on my brothers bike for him and forgot to tighten the bolts down just the top cap, and the next time we went out for a ride, he and i raced down to the traffic light at the end of our street and as he attempted to trackstand at the red his handlebars turned in the opposite direction of his wheel. the look he gave me was one id never seen before, fear, confusion, anger and relief, all rolled into one. i love my brother and would never want him to crash on his bike, but i dont think he believed me.

Which one? The GT? It'll be a little while, but within a month hopefully.

-Parking my bike in front of a subway station, not checking the quick release on the front wheel when I unlocked it at the end of the day. Popped a wheelie onto the curb arriving at my house, did a cartwheel across my front lawn.

-Replacing my brake pads, not tightening them enough. Watching my front brake pads come loose and spin around while trying to brake downhill.

-Not taking the bolt out of my crank before screwing in the crank puller...why are all these metal shards coming out of my crank?!

I decided to convert a schwinn traveler instead of just buying bd...

haha but really I like my bike a lot. When I first decided to convert I thought I would just do SS, but bought a SS conversion from performance only to find out there is such thing as a cassette and that it is different from a freewheel. Not knowing I could just buy a freewheel I bought a cassette rear wheel to use the conversion on. Dudes at my bike shop suck. It's all good though I threw that on my Gf's bike and converted it to SS and bought a flip/flop wheelset for my bike.

Also, I once tried removing the cranks with the bolts still on... I have no idea how nothing stripped, guess I'm a wimp.

I did this on my first ride around the block. I heard a little *clink* as I approached my corner, thought nothing of it, and kept going. I facepalmed pretty hard when I got back to the garage and looked at it. Then I spent the better part of an hour trying to find the damn thing in the dark (this was all at around 2:00AM).

I've put my toeclips on backwards or upside-down at least three times.

It took me a pretty long time to screw my pedals on the first time because "WTF, they're threaded the wrong way!"

Wow, I just re-read my last post. Apparently I hate to use commas, whatever, my bad about the stream of conscious typing. I promise I know how to use them, I just forget to.

Forgot to tighten stem before attempting to ride my first tallbike.

Had a really cheap chainbreaker, busted a couple chains due to bad pin installation.

Got a new Pista a couple years ago... make it about 20 miles before drive side crank arm came loose, still run it, but the splines are a bit marred and has very slight wobble. Lesson learned, check everything as soon as you get a new bike.

Loose chain, dropped it... unrotofixed cog, lockring threads toasted. Fixed/Fixed hub, tossed the cog on other side, peened lockring on with screwdriver and wrench, no backpedaling for the ride home.

Broke one of my first crappy booger welds on the first chopper that I build... about 15 miles from home. Rest of the bike was sturdy enough to ride it home.

I didn't use my a torque wrench for the crank bolts when I but a new crank set on my fixed gear. It also seems I didn't torque the chainring bolts enough. A couple weeks into the new set up I noticed my chainring was loose, while I was at school.

"F my stupidity" I said, and quickly pulled out my chainring bolt tool and tightened them down(yes I carry one with me). On the way home my non drive side crank falls off! Luckily I was only two miles from home so I managed to ride with one leg. I still had to go to the LBS for a new bolt though. It's a good thing I have clipless pedals or else that thing would have been thrown into the street and run over.

The minute I got home I busted out the torque wrench. I don't know what I was thinking when I tried to get those crank bolts tight with a little 6 inch hex key.

I had just built up a new bike, and was taking it for a break in ride, to get it all fit. I had the allen wrenches in my pocket so I could make the adjustments quickly. After a few stops to get the saddle height right, I wanted to lower the quill stem just a tad. What did I do? well, I wasn't going to stop, I mean the bolt is right there. I loosened the binder bolt while riding, and promptly flew into the curb.

When I was a kid, I had a junker 20" of some sort, and there was some other partial bikes around the farm. I decided to make one out of the best parts of all the bikes. I found a 3 speed hub, and a shifter, and started working away. (I think I was around 10yrs) anyway, I found I needed the longer chain off one of the bikes, and so I found the master link and took it off the donor.

Then I could not find a master link on the bike I wanted to ride, and having never heard of a chain tool, I decided to cut the chainstay with a hacksaw, confident my dad could weld it back together when he returned from work.

The bike was all built and ready to ride when my dad got home(except for the slice through the chainstay). I was proud of my efforts, but dismayed to learn, that you DO NOT put on a chain by cutting through the chain stay.

My dad was able to braze the thing together so in the end my confidence was not misplaced.

You just won the thread!

Flip flop hub changed tire put fixed side on think it is still freewheel
try to coast out of garage get lifted over handlebars.
Did save the bike from going down could not save self.

I just realized that one of the front dropouts on my cruiser came unbrazed. I don't know how long I've been riding it like this. Oh well, still alive.

1) Over-tightened the steerer tube bolt, ripping the threading out of the star nut.
2) Got my laces caught while riding my T1... not really mechanical, but still FML
3) My friend asked me to retension his rear wheel. No bike stand (I was at his house) so I just flipped it upside down. After retensioning, he asked me to degrease and clean his chain. At that moment I was checking the tension of the chain... seeing if I could pull it off. I was so shocked by his request that I turned around to the left, in doing so, my right hand went to the right, and was sucked between the cog and chain (since his bike was upside down). Ended up breaking my finger and cracking two nails.

Threading a friends fork with a very old cast iron steerer tube threader. Didn't have a vice or anything, so a friend and I just held on to either side and reefed on it. Twisted the arms on the fork pretty bad.

I replace my bottom bracket and chain due to a drive train creaking I could not get ride of only to find ot it was coming from the left pedal that was shot.

When I did that the wheel was spinning so fast my finger did a complete revolution of the chainring. Which put quite a twist in the finger too. That was over 30 years ago and I still shudder when I think of it.

2nd dumbest thing was when I tried to get a crank arm off with a Park puller. Crank wouldn't budge so I slipped a piece of tubing over the handle and reefed on it till the puller ripped out the threads. That's when I noticed that I had removed the bolt, but not the washer under the bolt.

Within the same month while I was cleaning my chain (before a long +50 mi beach ride and after) I got my right index finger caught in the chainring and barely nipped it. Nasty little cut. And the other nasty little bite on the tip of my left thumb. No stitches but there was an okay-amount of blood.

Ugh so dumb! I'm never ever going to clean my chain while its on my bike! Nowadays I just take the chain off and let it sit in degreaser overnight.

Darn, I have always been really careful about cleaning the chain on the bike after seeing the article on Sheldon's page. I can't think of any mechanical mistakes I have made, but it's never too late. The next bit of work I need to do is remove the cranks and bottom bracket so I can re grease the threads, I just need to get a crank puller.