How about a tie knife
Yessssss!! The uber-tactical-tie! Exactly what I was looking for. Thanks for pointing it out.
Kiddings aside, I have two knives that could be considered neck knives. The first one is a CRKT Stiff KISS I bought sooooo long ago (like 17 years or so) that I recently modded adding some home-made micarta handles (yellow denim fabric). It doesn't cut very well, but at least now you can use it without it digging in your hand. The seath is made of some king of inyection molded plastic. Retention is nice.
The other one is a carbon steel, cocobolo handle, kydex sheath knife I got during a Knifemakers Christmas Exchange... from a fellow in the Us (I am in Spain). It is has like 2,5" of blade or so, maybe a bit more. Hollow ground. Great cutter. I have worn it neck knife style under a loose shirt while travelling in Morocco in my van. Just for the hell of it. Not that I hactuall y had a dire need for it or anything.
I don't quite find them so comfortable. A folder works soooo much better for me.