Tristan Tate is ripping James Kennedy a new one ... blasting the "Vanderpump Rules" alum for deleting a photo of them together and caving to online backlash.

Andrew's brother unloaded on James on social media, explaining the lead up to their photo over the weekend in Las Vegas, which James posted and then scrubbed from his account.

Tristan claims James "begged and kissed my a** for 30 minutes straight and called me a hero. He knew EXACTLY who I was and what content I made."

That's interesting considering James said he was "unfamiliar with their content and the allegations against them" and "regretted" posting the photo.

Tristan then lowers the boom on James, adding ... "He's just a p***y who can't handle DMs from woke r******. F*** this guy."

As you know, the Tate brothers arrived in the United States last week after Romanian officials finally allowed them to leave the country. The brothers were charged in 2022 with creating a criminal gang and Andrew was also charged with rape.

Ultimately a court ruled the Tates could not be prosecuted because of a series of irregularities committed by the prosecutors ... so they were allowed out of Romania and flew to Florida before heading to Las Vegas.

Andrew and Tristan have consistently denied all the allegations against them.