Agreeing with ehBeth here -
It's normal to look at humans in the first place, if you like watching humans, for a lot of reasons. Liking looking at the people whose gender you are particularly attracted to is even more fun. (I caught myself looking at the guy in the Dos Equis ad just today..) I don't want anyone stopping me from doing that. How dare they?
Some of us are flirts, some aren't, but a great deal of flirtation is just playful and not to be taken seriously. One learns to tell the difference.
Staring and staring isn't something I take as playful/non serious. Invasive would be the word I'd pick first.