Shaquille O'Neal's name lends itself to plenty of puns and nicknames - Shaq Attack, The Empire Strikes Shaq, Shaq-Fu (that was a game for the Genesis / Mega-Drive, incidentally).
So it's no surprise that when Shaq and John Cena came together for Carpool Karaoke, the topic of terrible puns and nicknames came up. With credit to Cena, he had a few clearly pre-prepared for meeting Shaq. Not only that, Shaw was able to fire back with a few of his own Dad jokes.
"You've been served a sub-Cena." Excellent stuff. Take a look.