Kevin O'Leary was out in these streets wearing an outfit that provoked Don Lemon to catcall him from traffic ... as seen in a hilarious new clip.

We spotted the stars leaving legendary West Hollywood restaurant Craig's Monday night ... stepping out separately. While "Shark Tank" star O'Leary's walking out of the joint, Lemon rolls down the window of his SUV and yells out, "That coat is gayer than me."

The assembled crowd on the sidewalk breaks out in laughter, and KOL takes it on the chin ... thanking Don for the compliment before the veteran newsman departs.

The fluffy knit coat has a high sherpa collar sticking straight up 1980s preppy style ... and something about it clearly set off Lemon's gay-dar.

This is a rare moment of levity for Lemon, given the recent legal circumstances he's found himself in. As you know, the Department of Justice has charged the star with with conspiracy to deprive rights, and violation of the FACE Act -- interfering by force of someone’s First Amendment right -- after he covered an anti-ICED protest inside a Minnesota church in January.

Lemon pled not guilty to the charges and has professed his innocence publicly in the weeks since ... no laughing matter.

Clearly, his sense of humor hasn't been dampened though ... and celebrities should beware since he seems ready to dole out unsolicited -- but kinda legit -- fashion advice!