ive gotten it on my bicep before, it looked like a bruise but i hadnt been hit there, it was just a really dark blue mark, it went away after like 3 days though, no clue what it was.
yeah dude...i used to get that all the time from benching on a bench that's a little too wide and my lats pinch or rub on the cushion, i was baffled over it for a few weeks till my buddy worked out at the same gym once and got it after bench.
WM