I saw a clip of video titled “David Letterman came back to The Late Show this week,” on Time Magazine's website. In the CBC’s show, Letterman revealed that he was threatened by a jihadist lately. After joking he wishes the audience to be more like a human shield for him on the site, he said:
A guy, a radical extremist threatened me to cut my tongue up. I wished I had a nickel for every time a guy has threatened to cut.
I know a nickel means a small change, but small change wouldn’t save you from a great threat. What does "I wished I had a nickel for every time he was threatened to cut" exactly mean — particularly in contrast to the seriousness (or gravity) of likening the audience to the human shield of himself against jihadists even as a humor?