When your butt hurts from geeting fucked in the ass a lot or real hard.
Person 1: I gave this girl a buttache last night. It was so funny, she couldn't even walk straight.
Person 2: I had a buttache when I woke up this morning. I asked my dad what happened and he said I fell down the stairs.
Person 1: You don't have stairs in your house.
Person 2: FUCK!