TMZ Sports ran into The Miz in Los Angeles on Thursday -- prior to the tragic news of Bray Wyatt's passing -- and asked him about the budding feud with Knight, who we referred to as "popular."

"Popular? So popular that you're following him into the store?" Miz sarcastically asked.

"So popular that last year at SoFi [Stadium] at WrestleMania in LA, the guy's name is LA Night. He named himself after the city and he wasn't even on the show. That's how popular he is."

The multiple-time WWE champ continued ... "He's a fad. He's like a Napster, MySpace, Vanilla Ice, LA Night, they're all synonymous."

Of course, The Miz and LA Knight have been trading barbs on Raw. Knight has accused Miz of being washed up, and the longtime WWE star responded by describing LA as a "blip on the radar."

In other words, he ain't 💩💩💩!!!

In fact, Miz says he doesn't understand why people even care about Knight (and do they ever care -- he's huge right now with the fans).

"Honestly, I can't believe people are talking about him. He's a fad ... and I'm just sick of his, I don't know. I don't wanna do it right here, right now but it's like if he keeps disrespecting me the way he's disrespected me, he's not gonna make it to WrestleMania in Philly. Let's put it that way."

Those sounded like fighting words ... so, we asked ... "Is that a threat or challenge?"

"It's a promise!"