Most chain restaurants like Applebe's or T.G.I.Fridays will bring you a cake to your table if it's your birthday or anniversary. They will have a few waiters sing happy birthday/anniversary while the other diners look on, and of course bring you a cake.
If you want to scam a free cake, have someone in your party tell the waiters it's your birthday and viola, free cake. Obviously you can't do this all the time. eventually they'll catch on. You only have 1 birthday a year.
If you know someone who's dining out and without them knowing, have this done to them. They'll deny it's their birthday with everyone cheering on. If they eat at 4 different restaurants in a month, well they'll get 4 free cakes.
Another idea. Let's say Curtis Lee Jones takes Charlotte out to eat after a day convincing Roy that the FBI is gonna call him. Slip the waiter a 20 and tell him the couple are celebrating their anniversary. Tell the waiter they're Curtis and Brandy. When they take the cake over and sing "Happy anniversary Curtis and Brandy." Charlotte will wonder who Brandy is and wonder what Curtis is up to.
Alternately make a cake with the PLA logo or MajorLosers on it and tell the waiter it's Charlotte and Roy celebrating their anniversary.
Then later that night call Curtis and ask him he liked the cake.
MIB