dude 1: "Hey man how was your date with Tucker last night?"
dude 2: "We made it to the next level... He totally cocknosed me in the bathroom at Starbucks!"
It means: a mutant combination between cockroach and mouse.
Robin: So what was it, a cockroach or a mouse?
Lily: It was a cockamouse!
Robin: What?
Lily: It's some sort of mutant combination of the two.
It's as if a cockroach and a mouse, you know...