yo dawg i heard you like Call of duty / so i waited in the corner and shot you when you walked in
A Yo Dawg meme.
Yo Dawg is rapper Xzibit, host of MTV's Pimp My Ride, a show that famously added car stereos to cars and TVs to car seats. The meme jokes about that habit of putting things inside other things: "Yo dawg, I heard you like X, so I put an X in your X so you can Y while you Y." It's the meme for recursion, nesting and anything that goes one level too deep.