“You don’t wash the mushrooms? It says on the package, man, they might have poop or pesticide or whatever else.”
When we make something about the other person, telling them that they are wrong and, in this case, even disgusting, they are going to get offended and be less amendable to seeing your side and helping you out. They may get shamed into doing it, but I think this damages the relationship.
Just make it about yourself
"Hey, Im a bit squeamish about unwashed veggies. Do you mind if I rinse them for you?"
Gets the same point across, but makes it about yourself rather than the other person, so they have no reason to be defensive. They will also be more likely to open up to changing.