I have once.

It was a friend's party a few years ago. There was one girl at the party called Kate, she always wanted attention and was only here because her friend was hosting the party. She was in her underwear most of the time trying to get boys to look at her. Me and my friend hated her for being such so self-centred so we thought of a fun way to give her ALOT of attention. She stood up on a table in her pink thong and began to dance, I went on one side of her and my friend the other and using some scissors we'd 'borrowed' each cut one side of her underwear causing it to fall to the ground. Everyone turned and stared and it took her a few moments to realise what had happened and her face was priceless. Her face turned red and he ran out of the room poorely covering her area. We only got a look at her round behind but a friend remarked how she'd not shaved in a while.