Well, I'll give it a bash. What sort of creepy?
The lingering stares, inane chat, slightly in your personal space and checking out your boobs often enough that you want to say "Hey, my eyes are up here!"
This usually is totally accidental, brought on by a combination of inexperience, shyness, alcohol and sometimes body habits you simply don't like.
For the body habits, I'll give you an example - a friend of mine is 6' 6". To look less intimidating on nights out, he always tended to lean forward to appear shorter, which of course creeped women right out. Nothing creepier than a guy who hangs over you like an unstable cliff, looking straight down your cleavage, is there! Once he learned not to do that, he was fine - the discomfort gals felt went away and they were able to reallise just how funny and sweet he actually is.
The eye contact thing I have mentioned before - too much direct eye contact makes guys uncomfortable, yet we all know that looking at the gal we are talking to is good and shows interest. Combine that with the fact that boobs (of any size) do have a magnetic attraction for all guys and it certainly sends out the wrong message!
The sweating, heavy breathing, crudely sexually agressive type of guy. Players without any skill or empathy, basically.
Some guys are creeps, simple as that. They don't ever see you as a person, simply an animated doll or a scoring system, or a plaything to be used and discarded. Fortunately for gals, most of them have never managed even the touch of a living boob and mess up the approach so badly that they give you plenty of warning.
You have instincts for a reason. Use them. Listen to them. They are not going to be 100% right, but they are frequently more correct than either your heart or your mind.
Didn't help much, did it. Sorry, I don't know many real creeps, just the accidental ones.
Share your stories in the comments, and guy readers - weigh in here too.