P&P, if it only happened once I'd write it off as an isolated nut. Unfortunately, there are just too many people like this. After one of these fine fellows "accidentally" put a round through my Pachmayr pistol box while searching for the safety on his pistol, I resigned from the Ike's and pretty much started avoiding public ranges. I'm not there to validate their purchase decisions, feed into their delusions, or stroke their egos. If they ask--BEFORE they put a round through the roof over the firing line, or my equipment--I'll be happy to walk them through the basics of safety and how their new gun works.
Loren, better to say what I like about Glocks before getting into what I don't.
Out of the box reliability is good--real good. I've seen a lot of new Glocks go with 2 or fewer feeding problems in the first 1,000 rounds. The value of this shouldn't be underestimated, most folks never reach 1,000 rounds. If the folks from Alpha Centauri start throwing EMP-equipped zombie-virus-laden meteors at us and I only have time to grab one gun at a gun store, I want a G17 and every spare mag and round of 9mm 125 they have. Without thinking or wondering, I know it will work and I can't think of any other NIB semi-auto pistol that I can say that about.
Before things went nuts in the latest round of insanity, Glocks were fairly available, and relatively inexpensive. This made it easy to source one to experiment with new cartridges. I had a couple of 10mms, a .40, and a 357 Sig. I could usually pick up the gun and spare mags, shoot for a while, and recoup most or all of my investment when I sold or traded the gun. Spare mags are available, and not outrageously expensive (think "S&W 52" or "H&K P7").
Accuracy is normally OK for a service pistol. The regular factory sights suck, but consistently so: they weren't made for target matches. Glocks are a pain to test in a Ransom rest, but comparing loads from a benchrest is doable if not quite as repeatable. This often means you can quickly diagnose problems without a lot of work. When a friend can't keep 17 rounds on a paper plate at 25 yards, you can shoot it and see if his sights are off/ammo is not working for him/he's a lousy shot.
As for what I don't like. . . the safety (or lack of a safety) comes to mind, but for me this is a training issue. I've never limited myself to only shooting Glocks. I think if I did I'd get used to it. Maybe.
I'm not comfortable with the polymer frame. Yeah, I know all the wonders of Nylon 6 and Glock's special blend, but I've also had frame cracks and parts break off on guns that were relatively new (early 10mm, ), while I was still testing them with factory ammo to get the brass to handload. Necessity sometimes requires storing a gun temporarily under less than ideal conditions (in a car in a TX summer, or NoDak winter), and this accelerates decomp of plastics. It isn't ideal for the car interior, and the car interior isn't supporting a pressure vessel.
Over the years I've seen one broken gripframe (cop buddy said he slipped on some ice and fell down a couple steps), and photos of another. I've had mags crack (once I had to disassemble the pistol to get mag and ammo out). The mag problem is supposedly fixed, but it is something I'd always worry about. There's also been reports of some breakage around the mag well--chips or cracks, usually on older guns. In the back of my mind I'm going to wonder if this is due to aging of the plastic.
And yeah, most of this won't matter as much to someone who shoots occasionally and only owns one pistol (or all Glocks). They're just things I think about. As I said, I'm not a fan; that doesn't mean I don't appreciate some aspects of the design.
Then again, I've always wanted a COP derringer, so maybe I'm just weird.