David Letterman is not letting up on John McCain. On Thursday’s show, the CBS comedian slammed the senator again, commiserating with Paris Hilton and saying he felt like an “ugly date” because the GOP presidential candidate backed out of an appearance on the “Late Show.” Letterman was upset Wednesday when McCain canceled an appearance to deal with the economic crisis. After backing out of the Letterman show, McCain sat for an interview with Katie Couric, then didn’t leave New York until Thursday, further angering Letterman. At first, Letterman said, he felt like a “patriot” to let McCain off. “Now I’m feeling like an ugly date. I feel used. I feel cheap. I feel sullied.” Letterman described Hilton — Thursday’s guest whose celebrity was once used in a McCain campaign ad to mock Democrat Barack Obama — as McCain’s first choice for a running mate. To Paris, Dave said: “I heard he dissed you. He dissed me.”