Those dumb things that simply should not be, here’s a few of mine, what’s yours?
Manuals:
Web only - why in the actual fuck? Portable Document Format exists, use it.
Stupid colours and/or tiny fonts - not good.
One manual, 50 languages - separate them.
PDF - without proper index and links - just seems really lazy.
Midi:
It is a standard - adhere to it or just stop making gear with midi.
Samplers:
Casio SK1, a 1980’s children’s toy had 4 voice polyphony - but your modern one doesn’t? Back to the drawing board then.
Paltry memory/sampling time - your memory chip supplier is laughing at you, they thought they would be stuck with those old small capacity chips, but then some sucker came along and bought them.
Firmware:
Beta testers - If your launch firmware has obvious bugs, get better beta testers, or delay the launch so that paying customers don’t have to be beta testers.
Build quality:
Rubber coating - when you think it will give a premium feel, stop, it goes sticky, it’s shit, don’t use it.
Flimsy construction - spend £10 more on materials, the customer won’t mind paying, if it means the difference between feeling like a cheap knockoff toy or something that is solid.
User interface - if it is annoying to use get better designers, because that is a fail.
USB:
Connector - USB C or gtfo. (Or B for non portable stuff)
Compatibility - host, class compliant, should be standard now.
Noise - don’t expect your customers to buy ground loop isolators just to use your gear, isolate the audio ground in your product, even if it means having a small switch.