Ones that have happened to me:
Taurus 94: one chamber was improperly reamed, and the bullet didn't seat quite deeply enough. The case head blew and locked the cylinder up. I'm guessing that's why I kept having flyers while sighting it in.
Smith & Wesson 1911PD: the spring for the magazine release dislodged, making it impossible to remove the mag.
Springfield 1911: plunger tube wasn't staked properly and came off during a string. Safety kept flopping around like an angry dolphin.
Sig P220: locking block cracked, locking up the gun. And this was on one of the oh-so-precious West German ones that are supposed to be so vastly superior.
Colt Python: insufficient clearance between the forcing cone and cylinder face would lock the gun up within fifty rounds. Also plagued with constant timing issues.
Smith & Wesson 19: I was young and restless, and I thought that driving a 110gr .357 at ~1600ft/s was a cool thing. Until the forcing cone gave out, and I literally could not hit a 12" plate at 25 feet.
Marlin 1894 in .357: don't use .38 wadcutters. Trust me on that.
Ones I've seen:
Smith & Wesson 360PD: the barrel sheared off on the third round ever fired. I've seen that twice.
Smith & Wesson pre-Model 15: owner's brother made handloads using shotgun powder. Cylinder and topstrap blew out.
Smith & Wesson 29: squib load split the barrel from the muzzle to an area 1" forward of the cylinder. Owner had switched from shooting .44 Magnum to .44 Special and therefore wasn't alarmed by the reduced recoil and report.
Colt Defender: frame crack at 40 rounds. Cause? Repeatedly chambering and firing .40 S&W ammunition.
Browning BLR: drastic overpressure event from handloads. One of the most epic blowups I've ever seen. Wish I'd gotten pictures.
Numerous 1911's: user firing steel-cased ammunition. Rim locks up the extractor, requiring a vise and hammer to clear the malfunction.
I could go on, but that's all I can recall at the moment.
In the depth of winter I finally learned that there was in me an invincible summer.