cold frog
Someone who feels the cold more than others
I get lots of action in the winter because my girlfriends such a cold frog
Cold as a frog's tail
Equivalent to "Cold as a witch's titty in a brass bra." It comes from the idea that frog's don't have tails because they froze off.
"You better put on a coat", said my Southern Grandmother, "It's cold as a frog's tail out there."