If they forgot your present, it's probably 'cause they didn't expect you to make it this long

"Now, see, it's not usually unusual for someone to be conceived during a graveyard shift."

"But being conceived during The Graveyard Shift...?  Little bit less usual."

"I'm guessing alcohol was involved, yeah?  Well, chances are if your brain's shrunk enough to repeat your folks' mistake, your balls are probably shrunk enough to obviate any chance of success, so here---21st birthday drink's on me."