Prince claims "clown" Tekashi's recent testimony -- specifically the part about an attempted robbery of Rap-A-Lot reps last year in NYC -- is a bunch of lies.

The rap boss says he's been warning everyone for awhile ...  that if Tekashi "keeps campaigning with dumb sh*t that he was gonna get elected! Election Day has come and now I’m hearing lies he’s telling under oath about robbing me or representatives of #Rapalot."

J. Prince adds ... "If him or any of those clowns were to try to rob me or anyone from the #Rapalot family bad news would’ve beat them home."

In case you missed it ... during day 2 of 6ix9ine's snitch-fest, he detailed how his relationship with his former gang, the Nine Trey Bloods, began to sour.

He claims he was denied entry to a Houston gig in March 2018 by Rap-A-Lot peeps because he didn't "check in," and it cost him money. As revenge for the diss, the Nine Treys planned to rob J. Prince's people a month later in New York ... and Tekashi says they pulled off an armed robbery on Rap-A-Lot reps in the lobby of a building.

J. Prince says Tekashi's version of events isn't how it went down, and the gig he got turned away from was his son's party ... because they simply didn't want him there.

He says ... "Let this be a lesson to those who know better to do better because there was never a question mark in my mind that this kid #takashi69  was rat material that’s why my sons didn’t allow him to come into their party. It was never about a rat checking in with us."

As for that robbery ... Tekashi testified he was outside in a parked car while his former manager, Shotti, and other members did it. Surveillance footage of the incident was played in court.