And, no, this wasn't a random diss directed at the mayor ... there's some bad blood here.

The drama began when a fan sitting courtside asked Irving ... "Why you didn't play like this when you were on the Nets?"

The Mavericks star had a response ... "Thank Mayor Adams for that, bro."

Of course, Irving, an 8x All-Star, spent parts of 4 seasons with the Nets ... but despite having two of the best players in Kyrie and Kevin Durant, the team didn't win, and Ky was ultimately traded to Dallas last season.

Irving's response to the fan was certainly referring to Adams' COVID-19 vaccine mandate policy during the pandemic ... which meant Ky, who chose not to get the vax, couldn't play any home games (or games in New York).

Not having Kyrie was a blow to the Nets team on the floor during the 2021-2022 season ... but it was also the root of a ton of controversy, given the polarizing nature of the vaccine mandate issue.

Despite the shot during the game, after the game, 31-year-old Irving talked positively about his return to BK.

"I don't think about it too often now," Irving told reporters, adding, "Pretty much at peace with what happened and spending time here. I wish a lot of guys well and a lot of people that I've gotten a chance to get to know."

"Got to see a lot of smiles. Got to make some kids really happy and that's what this job's about."

Not everyone was smiling, though ... before Irving's shot at Adams, some fans booed their former star guard during player introductions.