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It doesn't matter that he's training with Hulk Hogan ... if rapper Riff Raff actually makes it to the WWE, he's got an ass-whooping waiting for him ... so says The Miz.

The WWE superstar was at LAX -- when he told us he's glad Riff Raff is pursuing his dreams ... but warned the wannabe that A LOT of people have tried to get in the WWE, and A LOT of people have failed.

In fact, Hulk Hogan recently told us several ex-NFL stars were told to kick rocks because they couldn't hack it in the squared circle.

Interesting connection between Miz and Riff ... they both started on MTV (Riff was on "From G's to Gents," Miz was on "Real World") before trying to make the jump to pro wrestling.

Obviously, Miz was successful ... and Hulk is extremely confident that Riff can follow in his footsteps as long as he takes it seriously.