Someone should really study the effect Donald Trump's presidential campaign has on retiring and retired late-night TV hosts.

David Letterman made a surprise visit to Martin Short and Steve Martin's A Very Stupid Conversation stage show Friday night in San Antonio, Rolling Stone reported, and he couldn't help but use his stage time to make fun of the outspoken GOP candidate.

"I retired and… I had no regrets. None. I was happy. I'll make actual friends. I was complacent, I was satisfied, I was content. And then a couple of days ago, Donald Trump said he was running for president. I have made the biggest mistake of my life, I tell you," Letterman said, producing an envelope with a "Top 10" list about Trump.

"Number 10: That thing on his head was the gopher in Caddyshack. Number Nine: During sex, Donald Trump calls out his own name," Letterman said.

His final hit, "Thanks to Donald Trump, the Republican mascot is also an ass."

Watch the clip below:

(H/t Rolling Stone)