For me, the worst was Equilibrium. Hands down. Netflix mailed it to me recently and I watched it last night. Just... terrible. They go into this whole deal about "Gun Kata", where you can become highly trained and predict where the opponents are going to be, and so you can therefore shoot him before he can and dodge his bullets. Here's the quote from the movie:
"Through analysis of thousands of recorded gunfights, the Cleric has determined that the geometric distribution of antagonists in any gun battle is a statistically-predictable element. The Gun Kata treats the gun as a total weapon, each fluid position representing a maximum kill zone, inflicting maximum damage on the maximum number of opponents, while keeping the defender clear of the statistically-traditional trajectories of return fire. By the rote mastery of this art, your firing efficiency will rise by no less than 120%. The difference of a 63% increased lethal proficiency makes the master of the Gun Katas an adversary not to be taken lightly."
Looks basically like a guy twirling around like a ballerina with pistols that never run out of ammo. It's really pretty stupid. I mean, you can just tell that that the guy who came up with that tripe doesn't shoot. And, turns out, the director invented the "martial art" in his backyard. Style over substance, and 100% lame. A dude behind some good cover a few yards away could easily take out the twirling nancy with like 3 rounds from even a reasonable carbine. How the hell could you hit anything within 5 feet, much less inflict "maximum damage", when you're doing cartwheels and handstands?
Best gun play in a movie might have to be We Were Soldiers. Toward the end, when they were being over run, Plumley just seems to have a way with the good, old 1991A1. Love the dialog, too:
"I think you oughta get yourself an M-16."
"Sir, if the time comes I need one, there'll be plenty lying on the ground."
A close second would have to be (yes, I know....) The Big Lebowski. When John Goodman is in the bowling alley pointing the .45 at Smokey, he racks it, shows trigger discipline, and then ejects the mag and live round in a safe direction before putting it in the bowling bag. Totally extraneous, didn't need to do it, could have just shoved it in the bowling bag ready to shoot his leg off... but didn't. I don't know why, but I was howling in the movie theater when I saw that scene. It's amazing to see hollywood get it right. (The safety aspects, not the pointing a pistol at your fellow bowlers. After all, it's bowling, not 'Nam. There are rules.) I suspect Goodman has shot a gun a couple times.