Robert Karageuzian is the founder of Pizzaboyzzz, an L.A.-based art collective known for its enthusiasm for pizza and pizza-themed merch, and he claims Jenner has burnt his brand by launching her own project with a similar name -- "Pizza Boys."

Karageuzian claims the trouble for him started in March, when Jenner, DJ Daniel Chetrit and Apple created an Instagram account much like his and even jacked his slogan -- "In Crust We Trust." He claims it led to his original Pizzaboyzzz Instagram getting shut down ... and he had to go through hell to recover the account and get his followers back.

According to the docs ... it was announced a few weeks later that Jenner and Chetrit would host a new show on Beats 1 radio station for Apple Music, called "Pizza Boys Radio."

Karageuzian says Jenner's project has caused massive confusion with his already established brand, so he sent a cease and desist letter on April 16 ... demanding they stop using the similar name.

He says they ignored his letter ... and continue to promote their 'Pizza Boys' show.

The Pizzaboyzzz founder is now suing Jenner, Chetrit and Apple to get them to stop using the similar name, and fork over some dough. Ironically, Karageuzian's Pizzaboyzzz Instagram account features a play on the popular Pizza Hut logo using their own name instead.

We reached out to Jenner ... no word back so far.