A cockblocker who prevents you from getting laid, or, if you are in the middle of sex they somehow ruin it.
Mark is such a fuck fucker, now I'll never get with Katy.
"Fuck Fucker" originated in England and has since caught on in the United States. It is a blend of "debbie downerness" and a distinct tendency to mooch.
Jeff, you are such a Fuck Fucker.