To be honest, I’d get annoyed if my flatmates washed my dishes, because I have a very specific way of cleaning them and also use my own sponge. I don’t really trust others to wash my things.
However, I also never leave my dishes in the sink for more than 10 minutes (will literally wash my stuff before eating), so there’s that.
Just wondering, how do you know that they’re mad? Have they directly told you?
I think they’re getting annoyed because either:
1. They DO take you putting their dishes to the side as being passive aggressive and by you also washing their plates, they feel like they are indirectly being attacked a bit.
2. They have no concept of time, which is why they leave their stuff in the sink for so long, but also like having their own cleaning routine.
I totally agree with you that this is gross and unacceptable. Some people do just live in toxic environments lmao and can’t seem to clean up after themselves. I would tell them about it, but try to present it in a jokey manner. When you are in the kitchen with them, point at the sink and be like “are you trying to grow a whole ecosystem in there” or something. If they return a joke, follow up with “no but really, that’s gonna get mouldy” or something along those lines. Usually, even just casually pointing out “dude that plate’s been in there for centuries” might do the trick. If the pile is very high, make it seem like you are REALLY struggling to clean a utensil because of it.
If all else fails, move the dirty stuff onto the counter and if they ask, be very apologetic and say “oh sorry, I just didn’t have space to wash my pan.” If they’re at least decent people otherwise, they should be more mindful.