i was playing with my brother in multyplayer when this happened. has it done before? why would this happen?

You hit your leg with your foot, then moved it around in a violent motion, of course its going to pop off :P

Oh, what a classic Taek Kyon moment... things like that have won me countless matches. Amen to them.

just a bit of the cruelty of self damage. your hip was already stressed after the kick (-> lessened DMtreshold), and then the momentum and awkward position rips it off. although rare, not completely unusual

...lawls, i can see who are the 3 ppl who are online and active at the moment lol...

lol happen to me once.