Here's Johnny Manziel takin' a big bite out of his fiancee's flawless ass during his recent trip to Mexico ... on what's now being hailed as the greatest pre-wedding vacation ever. 

Remember, Bre Tiesi included her future husband on a topless romp through the ocean with 2 of her equally hot friends during the amazing week long getaway.  

They've since returned from their trip, Johnny has resumed training for his NFL comeback.

Probably got a good workout in Mexico though ...