When you do things that make people think negatively about you, it's called "leaving a bad impression".
An "impression" is a quick decision that people make about you when they first meet you. People often talk about their "first impression" of a person:
My first impression is that he's a really nice guy, but perhaps a little difficult to get to know well.
The way that you act when you first meet people "leaves" an impression in their minds. If you say smart and interesting things, people will "be left with" a good impression of you. If you act rude, it will "leave" a bad impression.