Guys that treat the range like its their social hour. 2-3 minutes of talking is ok, but I didn't come to the range to talk. I came to shoot.
Guys that call the range cold every 5 shots so they can walk down and look at their target. I don't mind stopping every 1/2 hour or so, but any more often is just silly. Get some binoculars or a spotting scope if you *NEED* to see your target up close that often. This is probably a sign that you need to be shooting at a shorter range.
The "brass chickens" mentioned above. My brass is my property. If you take it, you're a twinkle toes communist manure sucking dirtbag thief who hates America and Jesus. Seriously, do not touch my brass. Don't even look at it.
Tactikool Ninjas who show up to the range looking like extras from an action movie. Yeah buddy, you really need hard-knuckle gloves and a plate carrier to shoot your glock at 7 yards. This is America, and you're free to look silly. I'm also free to laugh at you.
Also, those guys who assume any/all shooting has to be SD/HD training, and bad mouth people who don't DA their revolvers and bounce around during mag changes. You're just as bad as the Fudd's who think all shooting has to be skeet and sighting in deer rifles.
Mag dumpers. I have nothing against people who can shoot rapidly AND hit their target. But folks that pull the trigger as fast as possible because they like the noise/recoil annoy me. They damage range equipment, and shoot over the berm. Was nearly shot by one many moons ago.
Worst of all, the dudes who see target frames, and other range equipment as part of the target. There's a guy at every range, in every workplace, etc, who gets his kicks from breaking things. I wish he'd do the world a favor and break his own legs.
I'm a member of a private club, so I don't have too many idiots to deal with. If I had to shoot at public ranges, I'd probably give up shooting.