Is backshitting on coworkers a “normal” thing here?

We had a “shinnenkai” dinner and after it part of our colleagues left for a billiard. Turns out a sales manager guy (who i thought was a decent person) shitted almost everyone Who wasn't there. being cptsd and not very talkative at work myself, i almost quit saying anything except necessary in presence of that manager. soon part of office coworkers gonna have dinner again and i dont want to join. Guess this time ill be shitted on too. I just never faced such toxic work environments as much as here.