STUMPERS CIX

The expression, "HE'S ONE OF US," is supportive and affirming. By inserting two letters somewhere in this phrase and joining two of the  words , you can change the phrase to a new one, which is an insult. What are the two letters, and what is the new phrase?

HINT:
The two letters are DO.

Answer:

"HE'S ONE DOOFUS."

Credit: LA Times Crossword
January 10, 2010
Nora Pearlstone
JUST DO IT