Don't be afraid to be honest!
Most Helpful Guy
Most guys will tend to distance themselves for the girl in questions, if not completely avoid them. It's a natural thing we do if we dislike anyone, not just girls.
Other things are withdrawal, not as talkative around you, talk to others if they are present and things lke that
Most Helpful Girl
Either i tell them flat out, or negative body language. Ill avoid them, and basically dont want anything to do with them if theyre a stranger. If i know them... well id probably just tell them.