Letterman is just bitter because Leno has trounced him in the ratings for 15 straight years.
Via Newsbusters:
“Hey, you remember evil dictator of Iran Mahmoud Ahmadinejad?” Letterman teased. “Well, no longer evil dictator. They had election, and he’s out, and I was thinking, ‘Boy, you thought Mahmoud Ahmadinejad was in bad mah-mood before, he’s really in a bad mah-mood now.”
After a video clip introducing the new president of Iran, Letterman said, “Ahmadinejad is retiring. He’s going to spend all of his time on his ranch in Crawford, Texas.”