You know Jimmi Simpson from Psych, Black Mirror, and Westworld, but check out this compilation of his run as creepy Lyle The Intern on The Late Show with David Letterman.
Lyle would just appear in the guest chair randomly as a mysterious intern with vague duties, and attempt to befriend the famously reclusive Letterman in order to "break down your walls and get to your gooey cream center." He oozed with a strangely smooth confidence, enough to tell the host "I've cracked bigger nuts than you, bitch." And he only gets sketchier from there. It's weirdly compelling viewing.
Simpson told The A.V. Club that his friend Hank Azaria loved the bit so much that he made him work in an insult for him, which is why Lyle eventually starts referring to Dave as "Nancy Reagan." You'll see it all in this compendium compiled by Letterman archivist Don Giller, who even includes some unaired rehearsal footage rescued from a dumpster outside the Ed Sullivan Theater years later.
Andy Hunsaker has a head full of sitcom gags and nerd-genre lore, and can be followed @AndyHunsaker if you're into that sort of thing.