The former president's banter with a courtroom artist came as he made an appearance at his ongoing civil fraud trial in New York.
Outside the courtroom, the former president, 77, told news reporters that the trial was a "fraud" and a "witch hunt," repeating well-worn complaints that he is the victim of political targeting.
Inside the chamber, he appeared to be in a better mood as he viewed the work of sketch artists Jane Rosenberg and Isabelle Brourman.
"I gotta lose some weight," Trump said after viewing Brourman's portrait, according to the artist.
Trump is not known to lead a particularly healthy lifestyle. During his 2017-2021 presidency, his doctor encouraged him to lose up to 15 pounds by eating better and exercising.
He was found to weigh 243 pounds in a 2019 examination, which put him in the obese range, though his physician Sean Conley said he was in very good health overall.
In the New York trial, Trump's lawyers are trying to make the case that his company did not manipulate the value of its properties to win favorable financing.
The trial, which kicked off in October, is one of several legal challenges the former president faces as he mounts a comeback bid for the White House.
The judge overseeing the trial, Arthur Engoron, has already ruled that Trump and his adult sons manipulated financial statements to dupe banks and insurers into providing better loan and insurance terms.
Trump is due to testify on Monday for a second time.
His son, Donald Trump Jr., also has shown an interest in the courtroom artists' work. He told Rosenberg last month to "make me look sexy."