Rat

Either a person who is a snitch that is disliked by many, talking about people behind their backs and just generally being really sneaky, or someone who is considered silly or weird, but is called a rat affectionately by their friends

Person A: God, Nathalie is such a rat

Person B: Uh oh, what did she do this time?

Person A: Oh nothing, I just call her a rat sometimes because she's kinda weird, but I love that girl.