The founder of the hilarious game "Watch Yo Mouth" is on the attack after an impostor game started jacking his sales.

Joe Caiola is the mastermind of the OG game, where you attempt to talk to people with a cheek retractor firmly planted in your mouth ... this according to a new lawsuit. He says he got a trademark to protect his creation, fired up a website ... the whole shebang.

Imagine his dismay when he noticed another game on the market, called "Watch Ya' Mouth" ... which he says is almost identical. Even worse, Caiola says the people making the copycat game are shamelessly capitalizing on the success of his game, and cutting into his sales.

Caiola says he was inspired to make his game after seeing a movie -- presumably Melissa McCarthy's "The Boss," where she tries yakking with a cheek retractor. He's especially galled that the copycats told a story about how they created their game and then changed it to match his.

He's suing to put an end to the Johnny-come-lately game, and wants money to boot.

We reached out to the makers of "Watch Ya' Mouth" ... so far, no word back.

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