When you finger (preferably with your thumb) a girl in the asshole while she's driving and you are in the passengers seat.
I bet Finch gave Stifler's mom a nasty Hitchhiker's Thumb on the way back from that cabin in American Pie 2.
The Urban Dictionary Mug
One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.
Buy the mug