Green’s Dictionary of Slang

(US campus) a general superlative, used sarcastically.

1871		L.H. Bagg Four Years at Yale 49: Worst, latest, newest. A general sarcastic superlative, made popular by ’71. Anything, from a new hat to a society election or long lesson, is called the worst yet, the very worst, or the worst we’ve seen.
1997		T. Winton Lockie Leonard, Legend (1998) 65: ‘Worst,’ said Phillip [...] ‘Worstest.’ ‘Worsterest.’ ‘Worstedness.’ ‘Worstatious.’.