I'm small-busted, and there have always been men who will stare even at my chest, especially if I wear an open-necked top. I really don't think they realize how obvious they are. But hey, I've always enjoyed looking at physical beauty, myself, and I don't have a single thought about dragging some guy with cute buns or a sexy neck into bed with me. I just like to look. It's brain candy. I even take the occasional admiring glance at a gorgeous woman's face or figure. But I'm an artist, so maybe I "suffer" from excessive visual hunger that I can't really fight.
If it reaches a point of rudeness, I think you have handled it just right – pointing out the problem to the oggler's spouse or partner, or stooping down (jokingly would be effective) so they look into your face. I love it!
There's not really much point in becoming frustrated. We all have our needs for pleasure, and staring at boobs is apparently what satisfies some guys. I was very recently diagnosed with a rare condition that could diminish my vision or even blind me. I will deeply grieve the loss of access to physical beauty if that occurs. I hope I can transfer that need to music and touch if it happens.