This is going to be a two-way tie, going all the way back in the day....
1) Night-Ops Gladius.
This was a light about 15 years ahead of its time. Mine was stock. So, 80 lumens at the emitter. The concept for the design though was excellent.... except for that utterly garbage after-thought of a tailcap switch. It's like they spared no expense to make a SureFire Killer. But then ran out of money once they got to the tailcap switch. So, cheap plastic junk tossed onto the light. One, you can't even simply unscrew the tailcap to swap out the cells. There's a whole procedure involved. Get it wrong, you risk breaking the tailcap. Also, parasitic drain from the tailcap! The Gladius would ultimately represent a dead-end in flashlight evolution. When Night-Ops dropped it from their catalog, it would be replaced with a very conventional and very cheap re-branded, generic Made in China flashlight.
So, one night, I head out in the security patrol vehicle to get food at a nearby deli. (And yes, made sure to get permission first before heading out in the Security SUV.) Get my food, get in, turn the key, everything shorts out. So, I call for assistance. Another security officer comes out. We pop the hood to see what could be wrong. His light is tiny and weak. Out comes my Gladius. Took it to work for the first and last time that night. Output horribly dim. Cells should have been good. Then the light dies on me. Out comes my back-up light. Fenix L0D Rebel 80. (Thankfully, my emitter was good. That whole Rebel 80 thing is a separate scandal.) One of the absolute best single-AAA LED lights you could get when the L0D first hit the scene. Where the Gladius failed, my Fenix got the job done when it counted. Still have both lights. I'll give up my L0D when hell freezes over and Satan starts handing out free snowcones!
2) Pelican PM6 3330 LED.
"Garbage" is not even remotely good enough to describe this light. I owned it for about 10 or 15 minutes until the warped plastic body made it clear that inserting cells was going to be literally impossible! Outside of the body was fine. Inside was a completely different story. Plus, since I took it out of the packaging, I couldn't return it to the store I bought it from literally around the corner from where I dumped the pieces into a public garbage can! Pelican does make good lights. But this model is not one of them.