cakeday

The anniversary of a person's birth, traditionally celebrated with a party which includes cake, hence the name.

Me: Whoa Alex you're 24 today! Happy cakeday!
Alex: Thanks!

Cakeday Present

A variation on the dickroll popular on Reddit where a link to a user's "cakeday present" is really a meme of a naked guy who is presented as a "cakeday surprise."

It was the OP's cakeday, and he was dickrolled with a Cakeday Present.