Now that I think of it, that's also my experience. If I really need a project to do whatever (and can't implement the feature myself), I shut up, let the horrible attitude wash over me and put hours of effort into testing and providing helpful information, and maintainers usually mellow out eventually. If I hadn't done all of that work, the maintainer would have had to do it. Sure, they're much better equipped to do it and can probably do it in a quarter of the time it takes me, but multiplied by fifty tickets... Oof.

Being nice and professional just means smiling as you get a dumb request and being open about your intent to prioritize the request alongside everything else.

I can't second this enough, and it's the other side of that whole "put your code on Github and use it as a resume". If I'm looking to hire someone, and I look at their Github repository and it's full of nasty, unprofessional responses to PRs and such, it's a pretty safe bet I don't need that attitude on my team.