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When it's more than dumb... it's DUMBUH.

(the normally-silent "B" is pronounced, and "uh" is tacked on the end of it to emphasize the irritation in the speaker's voice)
MOM: "Why don't you want to go on the Harry Potter ride?"

8-YEAR-OLD BOY: "I don't wanna go on the Harry Potter ride because it's DUMBUHHHHHHH!!!!!!"
by Buster T. Foodcube May 17, 2011