I finally got the movie's joke!
After watching it at least 4 times before, I finally got the intended irony:
Lewis might lose his leg, certainly has permanent damage to it and to his machomania.
Ed got a hole in his back and belly from an arrow, and had PTSD for having to kill a man.
Drew plain died.
Bobby gets fucked in the ass, but comes out of it unscathed otherwise, almost like a hero.
The joke is: having to pick one of these horrible destinies (getting killed, losing a leg, hole in the back and mental trauma - or getting fucked in the ass), every straight man watching this would rather get anything BUT Bobby's.