So, you're on a team and one of your teammates is underperforming. We've all been there, it sucks, but you try your best to pick up the slack.

Or, you can bitch at them for playing poorly. "Go back to unrated!" "WHAT WAS THAT AIM? OMG!" etc, etc, ad nauseum.

Protip: When you start being toxic, you are actually impeding the person from turning it around and improving. Either they'll stop trying so hard, stop trying to help the team at all or, in the worst cases throw or leave.

In conclusion: Be better.