This will likely end in disaster. Let me go get some pop-corn, I'll be back in a min
Seriously though, go crazy on cake, ice cream, pastries, fries, candies, chocolate...Wash that all down with an epic milkshake and perhaps some whiskey. Oh, and get a few beers too. On my 24th birthday I had about 15000 cals, half of that was at an all-you-can-eat sushi joint and the rest was my mom's monster of a black forest cake. The thing looked grotesque in retrospect, covered in cookies and enormous chunks of chocolate...Sweated the whole night and hit a DL PR the next morning while feeling absolutely cracked out.
Cherish this day.