jerk
A rude or mean person who does not think about others.
The word jerk can also mean a quick, sudden movement, like when a car jerks forward when the driver hits the gas too hard, or when you jerk your hand back after touching something hot.
The word also has a completely different meaning. When someone acts like a jerk, they're being rude, inconsiderate, or mean in a way that makes others feel bad. A jerk might cut in line without apologizing, make fun of someone's mistake, or ignore people who are trying to be friendly.
As an insult, jerk is relatively mild. It's the kind of word you might use when frustrated with someone's behavior, but it's still disrespectful.