This ad starts out with Troy Aikman discussing football as Joe Buck starts dozing off, with his head nodding as he falls out of consciousness a couple times. Haddaway's What is Love? starts playing.
We then see various people nodding off: A guy with a combover at a diner, office workers, valets, cowboys, and nominees for "Song of the Year" award at a music awards ceremony (Busta Rhymes, LL Cool J, Macy Gray, and Missy Elliott). More people are nodding off: sheep shearers, Japanese restaurant workers, "Galacticon" convention geeks, a bobblehead factory worker, a game show contestant, and a father pushing his daughter on a swing, a trucker, and an auto mechanic. During the commercial, the father is sent flying as his daughter swings back and nails him across the playground, the auto mechanic doesn't awake to see that the has lifted a car up into a metal bar, and the diner man nods off into his soup.
Finally, an office worker pushes in a cart filled with Diet Pepsi Max. The office workers take a healthy gulp and are suddenly energized. Their sleepy head nodding suddenly turns into head bobbing to What is Love, a la A Night at the Roxbury. We see the various characters bobbing their heads now.
The true punchline of the commercial comes when Chris Kattan enters the scene, notices the head bobbing, and yells, "STOP IT!!!" at the people doing the head-shaking dance. Of course, Kattan popularized the movement with Will Ferrell in the Saturday Night Live sketches that inspired the movie A Night at the Roxbury.
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At the end of the commercial, an obnoxious voice yells, "Wake up, people!"