When playing on "Ranked" Servers, to gain XP for new cosmetics, there is no admins working these servers, so as above the only recourse is to just Leave. However if you play on Community Servers, where you cannot gain that XP, then more likely you will run into a Server Admin playing and they can help you more by taking care or booting the player then and there. Most of these troublemakers thrive on these types of servers, where there is NO Admins around to kick them off.
I HOPE there will be a "Favorites" Category in the Final Update, just like the older Insurgency has, because I hate sifting through servers each and every time I want to play. It is much easier to have one because each player in the game knows how their PC operates on that particular server, along with playing with something called "Friends" most of the time.