Johnny Manziel turns 24 on Tuesday ... and he's celebrating with a relaxing, peaceful vacation in Miami.
Just kidding ... he's pounding booze at 8 AM.
The ex-NFL quarterback has been partying in Miami for the past couple days -- probably because Miami is poppin' right now due to the Art Basel event that takes over the city.
He's dancing on yachts, he's hanging with celebs, he's been chillin' at fancy hotels.
Manziel has told us that he eventually hopes to get back in the NFL -- but it looks like the comeback is on hold ... at least until after his birthday.