When a woman's breasts hang so low down that you have to reach all the way down her top to grab them. Obviously, this is sexual harassment if done without consent, so don't do it unless both you and her want to do it.
Guy 1: So what'd you do today?
Guy 2: My girlfriend had a massive bag of tits, and I grabbed those puppies and smushed them!
well, ya see.. you have a bag. a dirty bag that is. and to make that bag dirty, you shit in it. then with your bag full of shit, you put the shit on the girls chest & moterboat it. good luck, have fun, & be safe.