LOL! the Benchmade 910 Styker that I carried today is literally the physical manifestation of everyone's deal breakers according to this thread (tanto blade, partially serrated, and tip-down carry only!)
In no particular order:
1. A weak detent - more of a safety concern for me.
2. Bad ergonomics - anything that doesn't feel right in my large sized hands.
4. Partial serrations on a blade less than 3.5" or so (on a folder).
5. Stainless steel handle scales - too slick!
6. Carbon fiber handle scales - they just don't do anything for me aesthetically.
7. Anything UNDER 2.5 ounces - super light weight knives always seem to wiggle their way out of my pocket.
8. Blade play, bad blade centering, etc.
9. Wire pocket clips...
I know, I know, I'm in the minority, but I can't stand them! In my experience, they always snag and and get bent out of shape, and they create horrible hot spots in my hand (which is why I got rid of my Spyderco Techno).