We use the same tricks, but I swear he learned it from me, and not the other way around. See, I realized that if I say, "can I sit with you, daddy" he will always say yes, and then he will say yes again, if I say, "can I sit in the seat by myself"
bingo, I've stolen the chair.
He's learned that he can say, "do you want to brush your teeth together or should daddy brush your teeth?" I'll say NO, but then he'll say, "ok then daddy will just brush your teeth," and then I'll say "let's brush teeth together!"