I don't know, maybe this belongs in the commuter's section because it happened while I was commuting. Anyway, I got out of work last night and tried to start on my way home after my bike being in the rack all day (first time parking there - and commuting - on a weekday, but have never had problems there on weekends) and my chain was making some weird rubbing noises. I looked down and my front derailleur was turned (not bent, turned) like 30-45 degrees from normal so that the tail end of the cage was up against the seattube.

I was like, "what the...?" and got my multitool out of my seatbag and loosened the allen bolt and turned it back to about straight the best I could (thanks to friction shifting for not needing precision). I'd tried turning it with my hands without loosening it, but it wouldn't budge, so I don't think somehow it worked itself loose enough that this happened on its own. I was at a complete loss for how this could have happened (and kind of grumpy about having to ride home with all my fingers black from chain grease - I guess that means I should wipe the chain down better, huh?).

Any idea how this could have happened? The rack area was fairly crowded (not racks so much as posts fixed into the cement with metal loops coming out of them at about the hight of 3/4 up the wheel). Could someone at the next post over have accidentally kicked in just the right place as they were getting their bike out to have caused this?

Would it take more of an intentional blow?

Is it something about my riding style that could lead to this?

Also, is it something I should worry about (bolts working their way loose - I didn't notice a nut -or now the clamp not gripping as tight), or is it unlikely to happen again as long as I tighten the clamp back up?

The bike parking area is sort of next to a valet stand, so I doubt a vandal just beating on bikes on the rack would have escaped notice.