My cousin fell into the habit of repeating everything he finds funny, to try and be funny himself. He basically has the mind of a child, so he doesn't understand the things he says, just that they made other people laugh at school, or it was loud and obnoxious on YouTube. It's lead to him saying some very inappropriate things to people and not even realizing it.
Some of the videos he's shown me that he really liked had some extremely raunchy content and he just saw there oblivious to it until some kind of slapstick thing happens, or someone shouts something loudly. My mom caught him watching nasty videos and punished him by telling him he couldn't watch that particular channel any more, but he constantly sneaked around watching it anyway, but it was obvious because he didn't understand that sound travels...
Luckily, his new favorite trend is just plain stupid rather than problematic. Now he just searches for overwatch videos where people set their sensitivity to the highest and just stand there flipping the camera around really fast. Of course, he has to imitate it too, because it seems he can't think for himself, and bugs me to constantly watch him play overwatch as he stands in one spot flipping the camera around and squealing with laughter. He fen gets mad that I stop watching after a few minutes, but it's the same thing everyday for like 20 minutes at a time. It wasn't even funny to begin with. Ugh, guess I went in a bit of a rant there.