Because if they do it in your chest, boobs get in the way and you might see it coming and be able to do something to prevent it.

Hee, yay for having to explain why I'm laughing in the middle of the school library.

Thanks. I'm not so much pissy now, as I found out that Alyssa, the one that was actually my friend, really didn't know what was going on. So I don't feel so betrayed anymore. Yay for that.