I can think of three talk show "incidents"
*Christina Aguilera on Ellen Degeneres
If you watch from about 4:00 to 5:00 she sure seems to want to tell us something about her husband.. ("There you go, baby!")
*The guy who did the sex tape with Kim Kardashian (some rapper I think) was on the Tyra Banks show, and she kept going on about how big he was, and how he must be extra popular with the girls now etc. Saw it on youtube, but couldn’t find the clip now..
*On Oprah, when Heidi Klum and Seal was there, Heidi told the story about when she first saw him, he was wearing tight bicycle shorts that showed "the whole package" etc. Almost made it seem like that was the reason they ended up together, although that probably wasn’t how she meant it.
Edit:
Jay Leno seems to pretty routinely do some size related jokes (often implying that he’s hung himself). Can’t remember that much on Letterman or Conan, although Conan had the Sausage Party bits a week he had only male guests. A bunch of salamis etc would come down on strings and an overdone announcer voice would do big penis word plays on the guests’ name etc. I thought it was pretty funny :D