Jon Stewart's David Letterman Underwear Joke Accidentally Mocks 2009 'Late Show' Scandal (VIDEO)

Jon Stewart was a guest on "The Late Show With David Letterman" Wednesday night, and while the two veteran talk show hosts had a funny and cordial interview, they found themselves in a bind when one of Stewart's jokes left Letterman blushing (and Stewart apologizing).

After some talk about GOP presidential candidate Mitt Romney, Letterman remarked that he reminds him of the men who pose for men's underwear packaging. This prompted Stewart to ask if Letterman himself even wears underwear anymore, then he launched into an off-the-cuff bit that quickly derailed:

"I would think at this stage of your career, you have people that could just sit there and hug your groin for you," Stewart told Letterman. "Just hold on. Just do that. You could have like a group of people --"

At this point, Stewart started losing his focus. Letterman's face became uncomfortable as he (and the audience) quickly realized that this sounded oddly familiar. In case you forgot, Letterman admitted in 2009 that he had sexual relations with female members of his staff, specifically his personal assistant.

"Jon, Jon, Jon," Letterman said after an awkward break for laughter. "I had a little trouble along those lines."

With both hosts laughing off the faux-pas, Stewart admitted that he had realized his mistake mid-bit but just couldn't stop. Watch the snag happen in the clip above or Click here to watch the full thing on YouTube.