I'm not sure where Gabe heard it, but we've had some episodes of him saying the word "stupid". It has been a totally incorrect usage, although one time he did call his sister a "stupid dog," but he said it in an affectionate tone. Almost as if he thought it was a term of endearment. Anyway, regardless of the usage, I've made it clear that it isn't a nice word, and is totally unacceptable.
Last night, we were getting ready for bed and he was playing with some little figurines, and one of the men referred to his toothbrush (I know, random) as stupid.
Me: What did you say?
Gabe: I didn't say it, the man did.
Me: Did you say stupid?
Gabe: The man said it, not me.
Me: Remember when we talked about how stupid isn't a nice word and we don't say it?
Gabe: (exasperated) I told you, it was the man.
Me: Well, the man is going to have to go away for a while if I hear that again. We don't say stupid, it isn't nice. It isn't a word we use.
Gabe: I'll talk to the man about it. I'll let you know what he says.