A replacement for someone's ex-
boyfriend or ex-girlfriend who looks so
much like the ex, it's uncanny. Sometimes done deliberately to
piss off the ex.
One Dude to Another: Did you see that chick with Nick?
Another: Yeah I saw her and did a double take, I thought it was his ex, not his new chick.
One Dude: She looks so much like his ex, she's a fuck-alike.
Another: Wait till the ex sees the fuck-alike. She will throw a
fit.