I didn't want to stifle creativity, but here are the insults I know:

I'd rather get laid than be eaten Your mother gives hummers to plumbers Your grandmother is so old she farts dust Your father wears knee pads to gay bars Your sister swims out to troopships Your brother fucks butterball turkeys Your sister turns somersaults on door knobs Your mother goes down on Egyptians Your brother's in love with a donut Your brother's father is a turkey baster In China, they do it for Chili Your brother's girlfriend is made of rubber

It's odd, but I'm finding that writing limericks is easier than finding humorous insults for the chorus.

Thanks for the few I didn't know.