The YouTube/boxing/WWE superstar got buck nekkid to celebrate 27 laps around the sun on Friday ... showing off his bod for his 22.5 million Instagram followers.

Of course, the Maverick doesn't show EVERYTHING ... he made sure to have a conveniently placed mirror covering his Mr. Happy area.

All of Logan's closest friends wished him a HBD in the comment section of his steamy post ... with some even jokingly asking him to start an OnlyFans page.

It's a pretty exciting time for Paul -- not only is it his birthday, he's one day away from entering the ring alongside The Miz at WrestleMania 38.

As we previously reported, Logan is taking his appearance VERY seriously ... and Miz said he's been absolutely crushing training leading up to the big match.

While Logan may not have too much time to party ahead of WM38, we're sure his bro, Jake, will help make it extra special ... as the guys posted pics together on a private jet as they headed to Dallas.

Jake also sent a special shoutout to Logan via Instagram ... sharing a bunch of throwback pics and even their oldest YouTube video together -- adorable.

Now, Jake would never pass on the opportunity to check out his bro's big moment ... but ya gotta wonder if he'll be involved in the event somehow.