Take a human whose birthday you are celebrating. Lift him about 2 feet in air by loosely holding hands and legs. Turn him upside down. Hit him on the buttocks with slippers, sandles, shoes, kicks, and anything that you can find — either till he starts agonizing or till you feel that you have had enough. Have him blow the candles from 2 feet away and (when successful) have him cut the cake. Put him down. Smear all the delicious parts of cake on his face. Emphasize on stuffing cake into body parts like nose, hairs and ears. Special points if you rub on eye glasses and dirty his clothings. Don't forget to waste as much food as you can. Bonanza if you drench him in the water, and even more, if you hit him when wet.
I don't know about you but that's how we celebrate birthdays in IIMA.
PS: Oh yes, don't forget to shoo your guests away too. Eat what's leftover of cake.