THE SNEAK ATTACK BUTT GRIND = NO
There is nothing more offensive than dancing with a group of friends, and having some stranger come up from behind and grind up on me. Like really? You don't even think I DESERVE to be asked? Because I really doubt my ass is begging for a grinding. (maybe some girls are... but not most I guarantee you) It's like, clearly we are having fun here dude - and maybe I would like to dance with you, but now you ruined it so don't bother asking.
Guys talk about how girls are so mean and we reject them all the time but I don't really think thats true. These days, it seems more EXPECTED than anything. Of course we are going to get offended and "reject" you when you just grind up on all of this. But its not even rejecting because you gave us no other choice.
What happened to the good ol fashioned "may I have this dance?"? Because chances are, you would surprise the girl - and she'd say yes.