Why is being hit on by guys you don't like "pretty hellish?" Last time I checked, it was flattering. You might not be interested, but if a guy approaches you in a decent and respectful manner, appreciate the gesture, be gracious, and take it as a compliment. As for picking up on cues and body language, making eye contact will tell you everything you need to know, and how to proceed...or not. That goes for whoever is initiating.