Two (insert racially insensitive word here) are shingling a roof, when one looks at the other one and sees him throwing away ever other nail in his box.
"Hey, you stupid (additional or repeated racially insensitive word), why are you throwing out half your nails?"
The other (racially insensitive word) replies:
"Because half the nails have the head on the wrong end!"
"No, you Frost-ing retarded (racially insensitive word) the first says: "Those are for the other side of the roof!"