When standing up, tuck your balls and dick between your legs (some call it a fruit basket) and pee. The urine will trickle down the inside of your legs, giving you an amazing warming sensation. Doing this in the shower is the cleanest option, but if your cold enough, anywhere else will do.
Tom: Man, i'm freezing!
Bob: Just do a Canadian Legwarmer, it'll warm you up!
Tom: Ahhhh, you're right, this feels great!!