A lot of Magic players in my group are more used to one-on-one than multiplayer. I'm not sure this is the case in your group. But what this often results in is an overreaction to ANY kind of board presence. In a duel, you pretty much systematically destroy/disrupt anything you can that your opponent plays. But in multiplayer, a lot of people don't understand that they need to prioritize because their answers are thinned out between a few enemies. So, they see somebody play SOMETHING, anything, and end up destroying it. Then, when somebody plays something that's actually a high-value target, they don't have the removal/disruption; they were too busy killing that team of mana dorks, just because because they were on the board.
A good example of this was recently, I had
Jaya Ballard, Task Mage out with
Magebane Armor. The mono-green player immediately shits himself,
Krosan Grips the Armor, and then the next turn the guy playing the
Sliver Queen combo deck goes infinite. It's not like we didn't know the Queen deck is a combo deck, either. That's literally all it does.
Unfortunately, there's not much you can do about this. Some people don't bother to learn from mistakes. Others just don't understand the dynamics of multiplayer well, often screwing themselves and the table. That's just the way it is.
Though I will say, I get super annoyed by the guy who is always sitting there screaming (usually with a shrill, cracking voice) "WHY AREN'T YOU DESTROYING THIS OTHER THING OH MY GOD WHAT IS WRONG WITH YOU GUYS". I often attack that player out of spite (but also often because they're trying to redirect attention immediately prior to their combo).
I also have a protocol when I play EDH. Attack combo deck, attack players with Islands, go from there. This might sound pretty stupid, but it's working out pretty well for me given the metagame.