This x 10. How is this so hard to figure out?
Be friendly with fat ugly smart girls.
Alright. This is a fair general assessment of reality. The truth is that men as a group do come off as slightly more...menacing and space-occupying, if that makes sense. if it doesn't, I'm willing to follow-up with better description. That said, when someone you are attracted to invades your space...brings their energy into your space with romantic intent, it is not off-putting or invasive (aside from the idiot who is just blatantly inappropriate/crass/vulgar).
On the other hand when an undesirable awkward icky boy or an older man takes you in with their eyes or tries to move in with a romantic approach, it's such a crossing of our more poorly defined feminine boundaries that it feels violating and disturbing.
And fyi: It is not unheard of that some guys also experience this violation when an unattractive woman makes an approach...it can both offend and disgust them.