When a man's penis enters his own butthole. This most often occurs by accident during an extreme sex act but has also been performed solo, hands free, by a very talented few.
Yo... I gave myself the loopty loop last night while pile driving your grandma.
When your driving and you don't know where you're going, and you miss the exit, and instead of saying u-turn you say you have to make a loop de loop. You say this so ease the pain of realizing you actually have to turn around. It sounds less harsh than having to take a u-turn.
I missed the exit! I just have to loopdeloop and then we'll get there!