ban list + mute list
Personally, I'd love it that you would be able not to listen to (mute) all the dirty scum players, you prefer. Also, it would be brilliant, if you could use a default IP / nick ban list by default when creating servers.
Therefore all the dirty, filthy nasty players you hate wouldn't be able to join by default.
For me it gets annoying where some old noob I don't remember just joins and tell me bad stuff like "I fuckered your mom noob!" and then I have to ban them over and over again.
So yeah, it's a selfish idea, but I found it to be really great. Maybe in the result the filthy players would have access to less servers overall and some of them would stop being so bad.