I'm not referring to getting a new player not familiar with everything yet. These guys will get the hang of it and it's good for us to be patient. This is due to new players=new interest=possible new content.
No, I'm referring to partners who: 1) Play Solitaire- do not help opponents and play as if they're the only one there 2) Insult types. There are some players who do nothing but insult their opponents. I'm embarrassed when I get one of these for a random partner. 3) Arrogant types who badmouth their own partners. They usually like to blame the loss on their partner despite the opponents playing great and the partner not making mistakes.
I get an arrogant partner the most often. They are usually the worst ones to get. If you make a move that goes against their dogma of MTG play, they throw a fit.
I'll give an example: Recently I was playing Monoblack. I had played the 2 opponents before and knew their playstyle and what they depended on. I also knew my deck had a ton of creature removal spells. One of the opponents summoned one of their "bread and butter" creatures early. I cast innocent blood to remove the creature. I knew it was no big deal as my hand had plenty more removal.
My partner said in team chat "OMG" and then quit. In truth, this betrayed a complete lack of knowledge how 2 headed or other decks worked and also lack of knowing your foe..
Another thing deals with instants. If a player casts an instant on their own turns, this isn't the end of the world. In fact, so many stick to the dogma of 'cast an instant only on opponent's turn" to the point they're making huge mistakes. I've been cursed out for casting a thunderstrike on my turn to power up a wee dragonaut.
Another example of how not casting it sooner can be a mistake: Player plays a pump creature, let's say a lilliana's Shade, on their turn, and have zero mana left over after it. Those stuck with the dogma would wait and cast a, let's say electrolyze, on the opponent's turn. What good does that do? the creature will just pump up where that damage doesn't take effect.
What another player should do is continue to play it out, except for playing with those of the insult variety, and then make a mental note not to partner with them again. I also do that if a random partner plays Crosswinds or Mana mastery. Play that one game and then leave. Do Not insult the other player, just leave and find another game.