When you ruin your 'bro's' chance of getting somewhere or something in life.
eg, a promotion, a new girlfriend even sex.
Bro 1: ...So anyway you want to head to my place, watch Zack and Mirri Make a Porno, then make out for a while?
Girl: Sure, i'd like that.
Bro 2: Remember the time we were in the shower and i commented that you were bald where your pubes are meant to be, was sooo funny...
Girl: Do you know what... I have a erm knitting class on at 2 in the morning sorry.
Bro 1: Thanks for the Assisted Bromocide
Bro 2: ...