Well, when someone uses an OU team against someone who specifically requests a NU/UU battle, that does make that person a bit of a jerk. There is no way to actually implement rules in things like the PSS, so we can only put requests in. It's like how there's no way to, say, request a specific Vivillon pattern on the GTS; all you can do is request one in the message. And even though there's no way of enforcing those things, people do get angry when their requests are not followed, and if the request is reasonable, it's just not cool to violate that request.
Emphasis on "if the request is reasonable". This brings me to one thing that grinds my gears: people unrealistically requesting shinies on the GTS. Especially if the person is already asking for a legendary in exchange for a Com Mon, adding the message "Shiny plz" is just a dick move. I've been seeing this a lot lately...