A drink rape is basically a fun and aggressive way to make someone drink if they are being slow.
Drink rape is accomplished in the following manner:
One person sneaks up behind the victim, putting them in the full nelson, and a second person simply forces booze down their throat by holding the cup/bottle to the victim's mouth and pouring it down.
Bill was being a pansy at the party last night so we drink raped him.
He thanked us later.