Berating your team gets you nothing
Even if your mid laner is 0/8 it does nothing to point it out, it does nothing to argue about it, and it does nothing to actively blame them. YOu can blame them internally, or vocally, but once you start typing you're now wasting your time, energy, and mental effort on, logically, nothing.
Being a dick isn't going to give them 8 kills. Being a dick isn't going to erase the gold they've given, and being a dick isn't going to better them in any way. Really your best bet is to just play as well as you can, and ignore them.
If you lash out at someone playing like shit, theyre not going to listen to you, even if you rile them up and upset them, theyre going to forget it a game after and just continue on how they are.
Actively find things that they do good and highlight those points, praise what you can, or otherwise reassure them that things might not be as bleak as they are. Positivity is infectious, and proven to improve performance in any field, art, gaming, work, anything. Positive reinforcement will always be more effective than calling someone a feeding shitter, even if they ARE. You can know and think things about them but during the game, just force yourself to be a happy camper and think positively, and then when the came is over, if you're really that upset about their score, take the replay file, follow their gameplay play by play, and roast them. Get a mic, and roast them, point out the stupid shit they did, but save it for AFTER the game.