The Brief: Boom means "take that."

Bluesquiggle
DEEP DIVE

“Boom” can be added to the end of an insulting phrase for emphasis. The word itself is an onomatopoeia, intended to resemble the sound of a final blow. People also use boom to definitively present a point. The word communicates decisiveness and a certain “case closed” or victorious attitude. Mic drop is a synonym.

Boom, roasted

A common phrase combines slang terms boom and roasted. To roast someone is to drag them or throw shade. The two words work together to highlight a particularly savage insult.