Here are my biggest deal breakers:
If you were to trace a line around the handle of a knife, that line would need to be at least 12 inches long before I would consider purchasing that knife.
I won't purchase a folding knife that weighs more than 5 ounces and I won't purchase a fixed blade that weighs more than 7 ounces.
For LH folders, tip down is a no go. For RH folders, tip up is a no go. For IWB carry, high carrying pocket clips (where a lot of knife sticks out) are a no go. For pocket carry, deep carrying pocket clips are a no go.
I won't purchase knives with custom or proprietary pocket clips, especially machined/sculpted ones. I want to be able to switch out the clips and continue carrying my knife without skipping a beat if something were to happen to the existing clip. (That's why my Ultratech is the earlier model that used the CRK type pocket clip)
If the balance point of the knife isn't at least close to the finger choil, then that's a deal breaker. For a knife that sees use I prefer the balance point to be there.
I won't purchase a knife using the following damascus patterns:
Razor Wire
Bacon
Mosaic damascus with faces or the American flag
Firestorm
Random pattern
Hakkapella pattern damasteel
Twist
Diamondback
Ladder (if it doesn't have a tight pattern)
Reptilian
Typhoon
Cheetah
Fade
Blackout
Lizard
Intrepid
Sweep
Whiplash
Various San-Mai damascus types
Blued damascus with a deep purple or fade color - yuck.
I won't purchase a knife with the bolstered look on one side and plain Ti on the lock side. I also won't purchase a knife whose lock side is visually busy and chaotic.
I won't purchase a knife with the 66+ HRC steels like YRX7 or Maxamet or the super wear resistant steels like S110-V or ZDP.
I won't purchase a knife with a carbon fiber or copper beryllium blade. Too much to go wrong.
Blade inlays are a deal breaker for me as I'm too paranoid about something happening to the inlays as a result of use or temperature changes.
Camouflage, C-tek & tiger stripes do absolutely nothing for me and I actively avoid knives with that type of aesthetic. Anything "zombie" related is a total eyesore and I won't own a knife with any branding, marking or coloration to do with "zombies".
PVD and Cerakote type coatings look and feel like paint and they are deal breakers on a knife. If I buy a knife with a coated blade, it's going to be a proper boron carbide or titanium nitride DLC.
If a knife has metal handles they cannot be satin or stonewash finished because of the discomfort and slipperiness in use.
To me, anything with copper or brass is tacky & ugly and is to be avoided.
Skulls and skull imagery. Tacky & ugly.
"Moonglow" or various other glow in the dark inlays, scales or backspacers. Tacky & ugly.
Serrations and guthooks are deal breakers, as are awkward or nonfunctional compound grinds.
I didn't have a problem with exotic types of hardware earlier (spanner, tri-wing, other proprietary) but they are now deal breakers. The screws have to be Torx, flathead, Phillips or hex.
I won't purchase a hawkbill unless it's recurved. I won't purchase a tanto if it is recurved. I won't purchase a recurve if the recurve is too deep.
I have a lot more deal-breakers, but these are the ones that will completely and immediately remove a knife from my consideration.
