Some men (and very, very occassionally, some women) enjoy IMPOSING. Imposing and flirting are not interchangeable. When a person backs away, tries to terminate an exchange, looks uncomfortable, appears uneasy...a person merely flirting person can see these clues and back off. A person who is getting a charge out of imposing will disregard these clues and press on, often seeming to enjoy the discomfort he is causing.
Sometimes when an imposing person is explicitly told to back off, the imposing person will act like he wasn't doing anything at all, or pretend he was merely flirting. At the juncture, a woman being imposed upon is likely to be called...names.
Flirting's great. Having a person socially and physically crowd you is scary and exhausting. Whether the person is 'hot' or not. Scary is not hot.