Ah man where do I start? Well just a few of the things that I hate, and I'll hold no punches back:
1. Flashlight engineers ignoring the battery safety specs in their designs (I'm talking about you Surefire).
2. Step down in lumens, as too many companies are gaming the ANSI FL1 Standard just so they can list super high lumen values and long runtimes. (again looking at SF, Olight and many other companies too).
3. Not designing flashlights that can use environmentally sound and economical NiMH batteries (all eyes on you Streamlight, and you too LED Lenser, get with the game as it's already 2019!).
4. Side switches, as they can too easily activate in a pocket. (Olight you are guilty as charged).
5. EDC lumen monsters, I mean really, other than showing off, no one has a need for such ridiculous output levels that overheat in seconds. (Emisar put your head down in shame).
6. Strobe and SOS, especially on small keychain lights (Chinese makers all guilty at one time or another).
7. Lights with internal non-replaceable batteries, no company should be selling disposable lights with a 6 to 24 month life. (Surefire again, Nitecore (you started this stupid trend), Olight, Streamlight, prob others too).
I could go on but those are the ones I feel most strongly about.
Edit: added 7.