Britney Spears is learning a tough lesson ... jet skiing can be fun, but it can also lead to an inadvertent butt floss. 

Brit was having some fun in the Miami sun Wednesday, and from the front she looked like she was maneuvering her ride like a pro. However, when she came to a stop, it was time to start the real work ... correcting a massive wedgie!

Hey, it happens to everyone ... but very few of us look as good as Britney when it does.