Floyd Mayweather says it's about time he partied with Johnny Manziel ... because he made a TON OF CASH gambling on the former Texas A&M superstar over the years.

Johnny Manziel told us last Friday that he was going to continue partying on his days off, no matter what any of us think.

We believed him. There would seriously have to be no more celebrations of any kind taking place anywhere on the planet before we would actually think that guy would give up partying.

So there really was no reason to run right out and prove it in the most high-profile manner possible.

But that's just what Manziel did. The Cleveland Browns rookie quarterback went out, found a guy people love to hate even more than Manziel and enjoyed a serious throwdown.

That's right -- Johnny Football and Justin Bieber, together at last.

And not only did Manziel party at the Biebs' Beverly Hills crib with Floyd Mayweather Jr. and a bunch of famous people I've never heard of, he also retweeted photos of himself with the whole gang for the world to see.

Now to save you all the trouble of pointing this out, I realize that, as far as we know, nobody actually did anything wrong (although TMZ is reporting that the cops had to come out twice, but only because the music was too loud but also because Beliebers outside were getting a bit too boisterous).

And that Manziel is behaving the same way many 21-year-olds do and has the right to do whatever he wants during his free time, which he has plenty of right now since the Browns are off the next couple of weeks. Etc., etc.

Honestly, I think he's actually quite clever.

In pairing up with a guy like Bieber for yet another massive blowout, Manziel found a way to give all of his critics a great big middle finger without really giving us the middle finger because that would give us a legitimate reason to criticize.