I and most of us I like to think have seen our teammate do a very stupid play and lose the round. I sometimes just curse at them in the most over the top way. It's funny and blows off steam if I'm really tilting. What I never do is press v and let them hear it. Trash talking your teammates makes them play worse and I've had my fair share of stupid plays. They also probably don't need your help knowing what they did was dumb as they just lost round so they're probably beating themselves up over it anyway. (Which they shouldn't beat themselves up as that gets us no where and you shouldn't be mean to yourself.) People who are toxic on mic are just assholes who are incapable or critical thought.