One of the worst things about toxic players is that my cousin is one. Thank God he switched to Fifa now, lol. Atleast he can't write/trashtalk now.
In general when dealing with these people, the best thing is to stay passive and not give them the satisfaction. In most cases, if someone says "Omg, you're retarded", I just say "Yes", or "You suck bro", I just say "Ok.". If he keeps on, I just stick on with the passive bullsh!t and they get even worse until they finally realise I dont give a fck and they give up.