The Zach Bryan and Brianna LaPaglia split just got a whole lot uglier ... with Dave Portnoy and Josh Richards releasing a ruthless diss track aimed at the country music star.
The song -- titled "The Smallest Man" -- dropped Tuesday night ... with the Portnoy and Richards continuing to show support for their "BFF's" podcast cohost following her bombshell split from Bryan.
In the song ... the duo makes reference to the country music star's 2023 arrest, being active on dating apps and accusing the singer of spreading STDs.