So if you're a girl, and you have ever gone out dancing, I'm pretty sure that you can relate to what I'm about to say.
Saturday night, my roommate and I went out to a nearby club, and while the music was not ideal, we kept moving. Soon, more and more people started showing up, which was definitely a good thing. Unfortunately, with more people came The Creepers! You know them; they're the guys who hang around the edge of the dance floor, maybe standing still, maybe doing their awkward little dance by themselves. Well, they kept their eyes on us, as we were relatively close to them, and they kept either trying to force their way into dancing with us, or they'd grab an arm and say something along the lines of "Heyyyy, wanna dance?" with the meaning in their voice indicating that they expected a positive answer.
Let me just put this out there: HECK NO, I DON'T WANT TO DANCE WITH ALL YOU CREEPY GUYS!
I don't know if there is some sort of rule book for clubs, but proper etiquette dictates that you politely ask a girl to dance. You do not grind up on her. You do not assume that she will say 'yes'. Basically, you do not act like a creepy jerk.