Are you dumb or are you stupid?

I just had the following conversation with my seven-year-old:

Kid (yelling): I am not going to tell you because you JUST WON'T UNDERSTAND.

Mom: Why don't you try to explain?

K: You just won't get it.

M: Why? Do you think I'm stupid.

K: No. You aren't stupid. You could be a little dumb, though.

M: What is the difference between stupid and dumb?

K: Dumb is when you just don't have as much brains and you're not as smart. Stupid is when you are dumb, and mean, and kind of a jackass.

M: You can't say that.

K: I'm just telling you.

M: So, do you think I'm dumb?

K: No. Not excessively.

At that point, I laughed until I coughed, and then I coughed until I peed a little in my pants.