As for why a woman would rather use chemicals (of some plausible variety) rather than jerking a many off: they want to rob you, not have sex with you. I'm sure if they could figure out how to have their cake and eat it, too, they would.

Chloroform is highly volatile and would last only seconds when heated to 37°C (nipple temperature) in the open air. It is also toxic by skin absorption and a proven carcinogen! So as well as simply not working, the girls would have to be out of their minds to even try it as they would certainly be risking a horrible death.

This is a case of Hollywood science stimulating someone's imagination. In real life it just does not work like it does in the movies!

Chloroform is very volatile and evaporates within seconds.
Furthermore, the extreme cold experienced due to evaporation is very unpleasant on the skin, and would feel like freezer burn on the nipples.
Having (accidently) inhaled large volumes of chloroform over the years (9 years as an organic chemist), i can confirm that this method of incapacitating men is not viable.

For those of you that want to believe it to be true and will argue the toss, think about this: when frogs are knocked out (then killed) for dissection, they are put in a small sealed glass jar with a substantial amount of chloroform, and they are not knocked out instantly. Therefore, if you consider a man, many times the aerobic capacity of a frog in a room (ventilated or otherwise), are they really going to pass out after a quick sniff of some boobs?

They use lip balm to stop the chemicals being absorbed by their skin.