The only scars I've got are kayak related (got sucked into a hole at the bottom of a waterfall; couldn't roll up in the aerated water. Had to bail, wound up getting washed down a class three rapid, banged up my leg). Oddly, I've also done the James thru Richmond at twelve feet and have no scars to show for it. Bikewise, two stand out:

Accelerating on a fixed gear down Richmond's Laburnum Avenue, and I snap the crank in two. Face plant into the pavement, Slide across road, band my hip on the curb. Pull myself off the street and wait for an ambulance ride. Thought I'd broken my leg, but was walking (albeit slowly) within 24 hours and riding again in 72.

First nice day in Wisconsin, early 80's. Had put the gears back on the bike and was blasting around town and campus. Tear around a curve; unfortunately it was in the shade and therefore icy. I go one way, bike goes another. Wind up walking off, albeit with my jeans completely torn away on my right leg.