Floyd Mayweather -- ON THE FAT KID DIET ... For Berto Fight

Screw the vegetables and protein shakes, Floyd Mayweather is LETTING HIMSELF GO for his fight with Andre Berto -- stuffing himself with ice cream and cake during training camp ... TMZ Sports has learned.
It's almost an INSULT to Berto -- since Mayweather was deadly serious about his diet for the Pacquiao fight ... cutting out anything that wasn't deemed "healthy" by his personal chef.
Mayweather called in Chef this weekend for a massive 30-person dessert party ... complete with cheesecake, cupcakes, brownies, cookies, cinnamon rolls, root beer floats, strawberry shortcake, peach cobbler, vanilla ice cream and more. Chef Q said,
"Pretty much anything you could name, I had it laid out."
And the best part -- Mayweather is still paying those gourmet prices. Chef Q added,
"I made $30,000 that night ... 30 people at $1,000-a-plate."
Not bad, Chef.