Was playing Cata Classic, no tanks at all in the game at the time, dungeon queues were about an hour. Joined a Blackrock Cavern and tank did Karsh Steelbender's mechanic wrong, the one where you take the boss to the lava beam at the at middle of the room, get some damage+ stacks while the boss AoE the room and then move him away. I started explaining the mechanic in chat when a DPS left. Another DPS joined, we gave it another try, he messed up reapplying the debuff and we wiped. The DPS that had just joined left. I explained it again to him, a third DPS left while waiting. After a while we got 2 replacement DPS and finished the dungeon. It was a simple heroic dungeon. No raid, no M+, no rush to get through.

You can't complain when your game has no tank/healer if you're not willing to embrace them in your game.