When a man shits on a plate and smushes it up to look like a cake then jizz's on the top to make it look like icing. Then scrapes the 'cake' on his pubic area and makes a hole in the middle and sticks his cock in the hole. Then he makes someone eat the 'cake' and then suck his cock as a treat afterwards.
A: " John gave me a birthday cake last night, it was my favorite flavor."
b: " Really? Did you get his treat?"
A: "Yeah, it was awesome. Have you ever gotten birthday cake'd?"
b: "No, but it sounds yummy."