It is slang for causing someone to have a mental problem. "stop talking about her weight, you will give her a complex" (anorexia?). "Don't call your child stupid, you will give her a complex" (an inferiority complex?).

Peter is correct. Omid is talking about a different meaning of complex.

Hello

Hi, Being complex means people have trouble understanding you. It maybe because you don't want people to know what you think our how you think or maybe your thoughts are all over the place. It's not exactly a bad thing but people like it when then can easily categorize you and when they can't, they give you the label of being complex. But from their point of view they are also right as it may become too hard for them to know what you want and not being able to predict your actions.