1. The act of revenge.
2. To return to a previous state.
1. As in the game of punch buggy, one would say "punch buggy, no backsies!" If you are punched back, thats defying the rule of no backsies.
2. Guy: I fucked a stupid cunt now whenever I talk to her she thinks she's my girlfriend. Once you fuck a bitch, there's no backsies.