it's no vandalism, it's done on purpose:
https://www.boringcactus.com/assets/site.js
// Never read Hacker News
// - Aphyr, "Hexing the technical interview"
if (document.referrer.startsWith("https://news.ycombinator.com")) {
document.location = "https://upload.wikimedia.org/wikipedia/commons/d/d4/Human_fart.wav"
}
this also mean that copying the link and pasting it in the address bar will get you no fart sound
childish behavior if you ask me