Just as a crowded subway car is no excuse for inappropriate touching, a crowded club or party isn't either. If you need to get past a woman in a crowded space, say "excuse me" or politely tap her on the shoulder to get her attention if she can't hear you. Grabbing her by the waist and holding her in place as you make a way for you to pass is disrespectful of her body and boundaries. Despite the close quarters in the club, everyone still has the right to personal space, and placing your hands on a woman's waist is annoying and grossly inappropriate.