I can deal with most but the "ultra-moe" voice that some characters have is super difficult to power through. This is actually from a game, but it's the worst example I can think of and always springs to mind:
https://www.youtube.com/watch?v=hfX37R0O4a8
Whenever a character with this voice checks in, it's time to check out. Nobody sounds like this naturally, in the history of forever, including today. It's a voice that only exists in anime.
There's a time and place for everything... but not now.