It’s called a whoosh. When a joke goes so far over someone’s head that the sound can be physically heard. And it sounds like: “Whoosh.”
Or at least that’s what they’re saying on Reddit. There’s a whole section dedicated to Internet documented whooshes. And they’re hilarious.
A lot of people out there just really don’t have a sense of humor. That’s why they get whooshed. They can’t seem to sense sarcasm or irony either.