The former president was in Washington on Wednesday to meet with the Teamsters Union, where he took some questions from reporters.
Among the questions, he was asked about the red spots seen on his hand a few days earlier.
The former president appeared not to know what the person was on about, and showed and waved his hands around to prove there were no spots.
When asked what the marks were, Mr Trump replied: “Nothing, maybe it’s AI.”
Mr Kimmel trolled the former president for his comment, pointing out that some people speculated the marks were “symptoms of syphilis”.
“In this case, AI stands for ‘an infection.’ I feel like AI is going to be his excuse for everything now,” he joked.
As well as the ironic red splotch moment, Mr Kimmel also raised questions about Mr Trump’s denial that he did anything wrong – despite court rulings finding otherwise.
At the same Teamsters’ event, a reporter had asked Mr Trump if he planned to use campaign funds to try and pay for some of the penalties in his New York defamation and fraud cases.
“I don’t understand,” Mr Trump said, seemingly confused at what the reporter was asking, which prompted her to repeat her question.
“What penalties?” Mr Trump asked. “I didn’t do anything wrong, and that’s been proven as far as I’m concerned.”
“Even when he is literally caught red-handed, he will not admit it,” said Mr Kimmel.
“All of a sudden, Mr I-aced-the-cognitive-test doesn’t seem to know what’s going on,” he added, reminding viewers of Mr Trump’s claim that he did well in a recent cognitive test, while his Republican candidate rival Nikki Haley said she was concerned whether he is “mentally fit”.
He continued that “as far as the court is concerned, you did do something wrong, and it’s gonna cost you around $83m” – referencing the defamation damages Mr Trump was ordered to pay to E Jean Carroll.
Yet Mr Kimmel sarcastically theorised that Mr Trump may be saying all of this on purpose.
“I see what he’s doing,” Mr Kimmel said.
“I know exactly what he’s up to: He’s like that mob boss who pretended to be crazy by wandering around the town in a bathrobe. He’s Vinny the Chin, is who he is.”