Bored on lunch, here's one I tell often.

Two hillbilly kids.. Darla and Buckwheat are at school The teacher asks Darla, 'How do you spell 'dumb'?"
Darla says, "d-u-m-b, dumb."
The teacher says, "Very good. Now use it in a sentence."
She responds, "Buckwheat is dumb."

"Now spell 'stupid'."
Darla says, "s-t-u-p-i-d."
The teacher says, "Very good. Now use it in a sentence."
Darla says, "Buckwheat is stupid."

Then the teacher calls on Buckwheat and asks, "Buckwheat, spell dictate."
Buckwheat stands up and says, otay, "d-i-c-t-a-t-e, dictate."

The teacher says, "Very good. Now use it in the a sentence."

"I may be dumb, I may be stupid, but Darla says my dictate good!"