Toxic is a term to describe negative behavior that affects the community in negative ways.
Unlike what the majority like to call bad behavior for people not worshiping their negative norms and site culture.
Examples of toxic behavior, anyone who supports a broken status quo, homophobes, transphobes, racists and the usual, both the obvious and the more subtle ones, people who are wannabe elitists and promote an environment of toxicity by refusing to invite classes or specs because the community opinion is that they are bad(Even though all classes can do all content decently if they are good), people who try to avoid any sort of conflict and fight in order to keep a negative peace going etc.
Aka people who are wrong but often the dominant culture deems them as normal and ok instead of trying to eradicate them.