I have been called a c*nt for refusing a take-back in a rated game, it was clearly a blunder by my opponent and not a 'mouse slip' as they claimed,
They then requested a take-back on every move before they left the game without resigning, to which I claimed the victory :)
However, for every nasty opponent I have faced, I have faced at least 10 good and gracious opponents, you can of course disable chat in your settings should you wish to do so. (along with take-backs) and so on and also block or mute players so you never have to interact with them again.
Don't be put off by a minority or a single player, Lichess is excellent (the best FREE Chess site on the Internet, imho )and whilst I will never be a GM I really enjoy playing here and hope you do too @Faccintopa