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.
by sarasplayroom.com August 29, 2010
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