People who argue and talk about real steel weapons in the context to airsoft. Just because AKs are considerabley reliable in real life doesn't mean your Cybergun AK is going to last you 30 years. Just because the L96 is a considerably accurate sniper rifle in real life doesn't mean your UTG L96 is going to be more accurate than your typical AEG.
People who show up to games trying to look badass and ex-military. Lose the sergeant's cap, stop smoking the cigar like Clint Eastwood, and drop the 1000 yard stare. You're not fooling anyone, pal.
Scopes on AEGs. Face it, your plastic pellets aren't going to go very far. These airsoft guns are not precision intruments. They don't make you look "cool." Don't spend $80 on a scope when 1/100 times, your bbs will not go where you have your crossair.
People borrowing your guns and then breaking them. I'm nice enough to let you try out my TM G3A3. The least you could do is take care of it. I really don't enjoy someone snapping off the barrel of my G3 because they decided it was a good idea to use it as a walking stick when trudging through mud.