What does it mean to Hit on someone?
It means to make advances; to flirt with a person with the intention of trying to get them to go out with you.
If you mean that someone was starting to merge into traffic and then they stopped and you rear-ended them, you would be at fault. If the person merging into traffic hit someone, the merger would be at fault because they failed to yield to oncoming traffic. These are typical scenarios. Other scenarios or circumstances may effect the outcome.
To hit below the belt means to hit someone in the groin. A 'low blow' means the same thing. The expression comes from boxing, but can equally applied to martial arts, football, and most other contact sports. Metaphorically speaking, hitting below the belt means to do something that is both hurtful and clearly unfair, such as lying about a friend, deliberately hurting someone's feelings, or cheating your way into a position (or a promotion) that…