Well... I have a slight shred of empathy for the girl, my bf's friends aren't too fond of me for various reasons (I don't drink too often, I don't smoke, I'm hotter than any of the girls THEY'VE ever hooked up with... ect), HOWEVER, I'm always down to have my OWN time and let him wander off with his friends and unless it's mah birthday, I'm cool with that. I don't know, I think just peeing on her in general would suffice. Like her foot. Or her leg. Act really drunk while peeing on her and she'll be grossed out and won't want to hang out when you're around. Then eat up all of your friend's time.