A short list of things that bug me:

• Barrels for .22LR that are longer then 16.5"-18.5". Long Rifle ammunition loses velocity beyond these barrel lengths and it makes what should be a short, light rifle unnecessarily heavy and long. If there is no legal requirement for a longer barrel, don't use one!
• Role Playing Games with wonderful settings where NPCs do things that are unsupported by the rules. Sure it's "Just" flavor text, but that it the stuff you use to get players interested in the game.
• The failure of the AR-180 and the lack of clones and "inspired" designs on the market. If it hadn't gotten stuck in the 1970s and 1980s it could be just as modular (or more so) then the AR-15 design.
• The lack of good UI design in cryptography software.
• Hardcoded wireless standards in devices that require your network to downshift it's security.
• The difficulty in getting people to actually use encryption. I'm looking at you government and large corporations.
• How Facebook has put itself into the middle of all interpersonal communications. It wouldn't be so bad if people still answered email or other messaging systems.
• The lack of detachable magazine fed pump action shotguns on the market.
• Fixed gear bikes without brakes. Single speeds are cool, but the constant spin setup is annoying and brakes are a safety feature.
• How Linux designers decide that you don't need UI for program settings. 
• When there is a background image (like the Windows 10 Lock Screen) you can't change
• Operating systems without workspaces/virtual desktops (luckily the big three all have that now. Thanks Windows 10!)
• The death of the Trackpoint keyboard pointer. Best laptop "mouse" ever, and perfect for coding, no having to move your fingers off the keyboard to mouse to something.