I've had it when I was a kid. Ah the good old days with the ps1 and X-men VS Street Fighter.
I think I got it because of the amount of frictition I was making while using the D-Pad coupled with the sweat my hands were producing while playing the game (I was about 8 and it was a hectic game at times). My thumb swelled up with blisters, so what did I do? I wrapped my thumb in cling-wrap (thing you use to cover food) and kept playing :D







