This subreddit has probably been linked outside of reddit more than even inside reddit. It means someone who didn't get the joke and took it seriously.
If you encounter someone in Youtube or any other social media who didn't get the joke, just say 'That's the joke' instead.
This subreddit is known for its people posting comments (mostly on Youtube videos) and it is somebody saying a joke and the little kiddo who doesn't understand the joke says your wrong then they fight to the death or something. The subreddit description says "A subreddit about people who miss the joke/satire." and that's what the subreddit is about.
William: HeyOliver look at this it looks so real!!
Oliver: *looks at Williams phone* That's a plastic dinosaur. Are you ok?
Just a simple 7 fucking letters that make braindead people so confused that they go crazy not knowing what it means. They either beg the person who said it to tell them what it means or have to go to the deep deaths of the internet. It means that you didn't get the joke you braindead ape.
Guy 1: Wow! That guy is such a hottie
Guy 2: No you dumbass, this is the top 10 UGLIEST people Guy 3: R/woooosh
Guy 2: Legit just trying to explain to you that hes not hot
Guy 3, 4, 5, 6: R/woooosh