Bark collision.

It's funny how as we grow older we block out certain bad memories. Let's say for example, you were absolutely horrible at pee-wee league baseball. It is conceivable then that you have replaced these memories with ones where you are not quite so bad. Hell, maybe even average. Then let's say you join a softball team . Despite aiming at a person and throwing the ball directly towards them the ball repeatedly veers 56 feet to the and 43 feet above them. Then let's say you are playing outfield (cause outfield is for people who suck, you can do the least amount of damage there) and you are running backwards hoping to catch a fly ball that you know you won't catch. At the last second you turn and

BAM!

You run into the 1 tree near the outfield. Then let's say it leaves a big scab. Luckily you have a diskempt hair style which hides it though. That's always a plus.

The next day you may feel slightly inclined to pain when moving. Luckily you spend 10 hours in an office chair which your butt, after four years, has taken the shape of.