Anyone whose seen the Back to the Future movies multiple times can probably recall Biff's (Thomas F. Wilson) predilection for not just mixing but completely butchering metaphors. So I've been thinking a bit about this... is it possible to butcher them even further... and the answer is absolutely!
"I'm going to make like a tree and take a long walk through the screen door on a submarine."
"That makes about as much sense as an attic in a helicopter."
"He's knitting with only one needle in the water"
"He's not rowing with a full deck"
A personal favorite of mine was in the movie Can't Hardly Wait when the drunk geek is trying to console the equally drunk jock who is his sworn enemy:
"You know what they say about women and trolley cars? There's plenty of them in the sea."
C'mon use your imagination, get creative-- butcher a few metaphors of your own. Hit me with your worst!