Video camera mounts. Handlebar mount nuts and bolts weren't captive like my other mount, lost 'em immediately in the dark. And the helmet mount broke on the second use. Most mounts included with low priced video cameras are crap so I wasn't surprised. I always use backup lanyards for video cameras because the mounts are so bad.
Wahoo Fitness ANT+ case for my iPhone -- USB port broke within a couple of days. Same with Mophie Juice Pair Air. So I have to remove the phone from both devices to recharge it through the original Apple cable. Makers of otherwise useful doodads for iPhones can't seem to put together decent USB ports, so the entire device is basically crippled by a single cheap component.
Rubber band mounts, whether OEM with the light or other device, or aftermarket rubber bands. About half fail on the first use. Most fail after a few uses. I switched to rubber block/velcro strap type mounts like the Two-Fish for my Light & Motion Urban light. And use backup lanyards for anything that's expensive to replace.
With tires, so far, so good. I avoid tires with too many user reports of sidewall failure. I can deal with puncture flats -- that's so variable according to riding conditions. But sidewall failures? Nah. Unless we're riding through an obstacle course with razor blades at curb level, that should never happen. I've had good luck with Conti's cheap Ultra Sport II tires. Can't see paying more for GP4ks and GP5k with the reports of premature failure. I'm not strong enough to take advantage of a couple of watts difference. I rode Schwalbe One V-Guards for a year and while they were nice tires they cut way too easily. Not many puncture flats, but they cut like Henry Cooper's face under Muhammad Ali's gloves. Had to retire those Schwalbe's long before the tread was worn out.