Yes I find it completely rude. I guess like you said we pay for the server put our hard work into it with plugins permissions and such and every player that comes on thinks they deserve staff. The truth is once they usually get staff that's when they stop being good players. I know this isn't all cases. What really is upsetting is when you say no you cant have staff that's when these little 10-12 year old's think they have the right to cuss me out for saying no like i've personally been rude to them. On my server you cant have staff unless i've known you for a long time, trust is earned.
Basically there is always gonna be people who think they deserve staff but the longer you have a server the more those people sorta just seem ridiculous and i don't get upset anymore. Best way to handle it is be as nice as you can be and tell them i only except players who have been on server a long time and I trust.