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.