Foster's Home for Imaginary Friends - Sure You Can't Wilt
At the part where Frankie asks Wilt to do laundry, he says "I'm putting my foot down, no more mister nice guy!" He said the word "No". Later on, we learn he cannot say no. How is it possible for him to say no there?
Wazoo is right, it refers to the fact that he can't deny or refuse, Wilt is too nice and can not deny or refuse (think about it, he holds the door open at the mall when people are rushing in an out in one of the episodes, he is unable to get into the mall, but he can't refuse the person to pass before him), he can technically say the word no (honestly, who can't?), so he can use the word no in a sentence, he just struggles to say the word no when referring to denying something, because he doesn't want to be rude