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touch their boobs!! if they can touch you, you can touch them! only then will they understand that in order to touch you people must first act... plus it'll make for an interesting scene if you're in a public place :o)
That's wicked! I hate it when people do that. But assaulting them in return by grabbing their boobs is overkill. I think the best reaction is to ask them not to invade your space. If possible, let them know you need your space BEFORE they invade it.