The trend where some sections of youtube have random music loudly playing over what they are talking about.
Related: When youtube videos of video games don't use the in-game audio, and instead use unrelated music. (This is an immediate turn-off for me.)
Also, regarding things that turn me off from youtube video game videos:
* Bad aspect ratio, specifically when the video is in widescreen and is of a game not meant for widescreen (older games, especially an issue if it's a game boy (!advance) game)
* Effects like fast forward, siow down, zooming in.
* Cutting important parts out of the video (like the first encounter with part of the level, or a random encounter that causes a party member to die, forcing the player to return to the mosque before continuing).
* Video starting with loud talking, before I have a chance to stop it. (Autoplay is also obnoxious, but that's the site's fault (and partially the fault of web browsers and modern web standards), and not the video creator's.)
* Video ending with unrelated music, especially if it is the sort that gives me headaches. (If the in-game music gives me headaches, I likely won't be watching the video in the first place.)
* Races. I prefer to just watch one person playing, and I don't like the effect that competition has on play style and (if applicable) commentary style.
* Streamer singing along with the in-game music, or singing in general. (Singing is acceptable in music videos, of course, though I tend to prefer instrumental music.)
* Streamer referring to the audience as "guys". (This is particularly obnoxious when pared with the loud talking at the start of the video.)
* Even worse than the last one, streamer referring to the audience as "boys".
Another thing: I wish that videos would be clearly labeled as to whether they have audio commentary, and in which language they're in, so I don't have to guess and possibly find that the video is not what I'm looking for. (I avoid non-English commentary, and I often prefer no commentary to having commentary, except in special cases.)