The full stops represent the way Comic Book Guy says the phrase, with a distinct pause between each word. It distinguishes this quotation use from just any old utterance of 'worst X ever'.
What do you do with them when the X is more than one word? These two tweets illustrate the difference. This one gets it wrong:
While this one gets it right:Worst. Perfume. Name. Ever. pic.twitter.com/9dSIMx3MWf— Joe Harland (@TheJoeHarland) October 8, 2016
If your X is more than one word, you can't put full stops after every word. The full stops represent pauses, and you don't pause in the middle of perfume name and Tinder bio. They're intonational phrases, spoken with a single intonational contour.Worst. Tinder bio. Ever. pic.twitter.com/70NPFlzlO4— Sam Parker (@samparkercouk) July 1, 2016
I slightly suspect it might be different with a phrase where the stress falls on the second word, though. For example, Worst. Jacket. Potato. Ever. seems to work a bit better (though Worst. Jacket potato. Ever is still best in my view).