Actually, I've heard this word before. I've only heard it used for people who claim to be polyamorous, as a response to them, though. I've never heard someone say "Hey, I'm a polyfucker". So I can only assume it's a derogatory term for those people who use the word "polyamory" to get in someone else's pants, or as an excuse to cheat.
Me: 30F, straight
Seamus: My husband, 32M, straight
Dragon: My boyfriend, 29M, pansexual, married to Fox
Fox: My boyfriend, 29M, homoflexible, married to Dragon