Not 100% sure what you are asking so I have a variety of answers.
Firstly, one thing that has pissed me off in the past is guys who are only friends with you while they think they have a chance. If the guy has blatantly cracked on to me and I have turned him down and that has been that , that's fine. But when a guy begins cultivating a friendship, hangs around for months being mates and then disappears when I get a bf (I lost a heap of 'friends' when I fell pregnant), that just makes me feel like I'm nothing more than a vagina (since visiting this forum I have come to slowly realise that there is also the possibility these 'friends' disappeared because they liked me too much but I'll never know)
If you are asking where the line is between being interested and being creepy is, well that differs from woman to woman. Generally saying to a gal "you have a nice rack" is going to get you slapped. Saying "That woman has a nice rack, much like yours" is going to make some girls uncomfortable, it will make other girls blush and giggle, others will simply roll their eyes.
It's a hard question to answer as well because in my above example the second comment could get any of those reactions from me depending on who says it.
'People are never perfect but love can be. People waste time looking for the perfect lover rather than creating the perfect love' - Princess Leigh-Cheri from Still Life With Woodpecker.