If you can’t beat ‘em, joke about using your audience as a human shield against ‘em. David Letterman death threats may have popped up last week courtesy of an online extremist, but the late night host brushed off the news in last night’s monologue, joking that it was yet one more risk of being David Letterman. “I wish I had a nickel for every time a guy has threatened to cut my tongue out,” he remarked wistfully. For a sense of perspective, Letterman also aired a David Letterman enemies master list. The only surprises? Tony Danza and walruses. Once you lose the walrus community, I would have assumed the advertisers will follow.