The Brief: To "clown" or "be a clown" means to act foolish – like a clown.

DEEP DIVE
‘Clown’ is a slang term meaning ‘fool.’
When you entertain a clown you become part of the circus
— Khaled Beydoun (@KhaledBeydoun) June 24, 2019
“I just took a DNA Test turns out I’m 100% a clown”
I JUST TOOK A DNA TEST TURNS OUT I’M 100%
A CLOWN
— manicpixiememequeen (@mpmemequeen) June 20, 2019
“You’re a clown if you flex on the people that helped you in your time of need.”
You’re a clown if you flex on the people that helped you in your time of need.
— U S M A N (@Donjonn22) June 24, 2019
The phrase “putting on clown makeup” means to act like a clown. It’s often used in reference to someone who is acting foolish despite their better judgement.
i really miss my boyfriend and i said i’m not gonna text him til he text me first but looks like i’m putting on my clown makeup soon
— SAINTIANA (@rivermoon98) June 19, 2019