The name refers to a digital file that allegedly contains a "cursed" or highly disturbing episode of SpongeBob SquarePants . According to various internet myths:

If it’s a video file, it is likely a "screamer" or a fan-made "analog horror" video intended to be disturbing.

If you encounter a download link for this specific file name:

In actual internet history, files named "Krusty Krabby Patties.rar" found on peer-to-peer (P2P) networks or sketchy forums were almost always malware, trojans, or "screamers" (videos designed to jump-scare the viewer with loud noises and scary faces). Why It Spreads

Krusty Krabby Patties.rar -