Let's see, it all revolves around not reading the basics first.
Showing up in clothing that screams "I'M HERE!!!"
Shooting everything that moves, friend, foe, leaves...
Yapping so much that even if you miss the funky clothes, you can simply aim at their voice and hit them all (they gather in bunches).
Yapping when 'dead' so much that players still in the field cant hear anything else.
Running screaming across the field saying "You cant hit me!"... two seconds before they swallow a BB.
Shooting your partner, the guy who'se right behind you covering your ass. (I know, said something like that already).
Removing goggles, usually a fraction of a second before you get a burst in the face that was launched your way 2 seconds ago...
Extreme stupidity with loaded guns in the staging area.
Truly stunning mechanical ineptness (watch a newbie open a mechbox for the first time when they claim they know it all. To add insult to injury, watch this happen outdoors at a staging area. Much fun ensues).
Getting lost in a 4 acre woodland, when to the immediate north is a major road, and in any other direction is a swamp. (What do you mean you're going into woodlands and cant tell where North is?)
Showing up to a game with everything imaginable, except a charged battery.
Of course, again, never Ever reading anything.
Oh, by the way... I've personally witnessed all of the above.
Honestly? If it's totally stupid and moronic, it's been done.