I see the word "toxic" everywhere these days, it's the new hashtag to describe someone who's behaviour is not quite to your liking. A while back it was the word "racist"
A toxic player to me is someone who purposely goes out to insult or harries other players in some way. I assume everyone else to be just having a bad day or are preoccupied. Something we are all familiar with
I feel for those who get labelled as toxic for the wrong reasons.
A example of a real toxic game community would be Eve-Online. Wow, I met some people on there that were borderline evil.