From Wiktionary, the free dictionary
From lil + bro.
lil bro (third-person singular, masculine, nominative or objective case)
- (African-American Vernacular, slang) diminutive of bro: he, especially in regard to someone smaller or younger.
2023 February 5, Crim (@Crimisum), Twitter[1]:lil bro is hard asf
2023 February 3, ZERO CHILL FIGHTS 🥊 (@zerochillfights), Twitter[2]:Lil bro ain’t to be messed with
2023 February 2, OJSpaceMan (@SpacemanOj), Twitter[3]:Lil bro’s Fortnite accent goes crazy