Never ask any of that stuff. A famous ballet dancer once said that the only way a performance would get off the ground is to fall a little bit in love with your partner for an hour. This "hobby" is about sex, passion or the illusion of romance. If you want lunch counter conversation get a dog or rent a friend.
However, just the other day I asked a lady with a very bodacious set of ta tas how she got them in that nice designer bra in the first place. I think I actually said "G*d damn, how do you get those things in that bra?!" and she didn't seem to get pissed off or anything. I meant it as a compliment.