"You don't wash the mushrooms? It says on the package, man, they might have poop or pesticide or whatever else."
"Okay, well if I'm gonna be eating them can I wash them? I'll make 'em up, man, I'm not telling you what to do. But I don't wanna eat anything that's on them that might be bad for me. I would prefer not to at least."
I don't know, you can adapt the language, or stay away from the whole conversation if it really feels wrong. But usually if there's an issue it's better to say what the issue is even if it's a little uncomfortable. You're not making a problem or starting a confrontation, it's just saying what's on your mind and sharing. Otherwise you don't really have friends and allies, just sort of alien people you're going through the motions with while you each harbor your own little secret thoughts all through the evening.