I haven't tried carrying a knife around my neck, and I'm not trying to offend any folk who do, but I had rather not. There is not only the sharp knife, there is the issue of a loop around my neck if I were carrying a knife in such a way. A cousin of mine nearly hanged himself in such a manner. He was going down a wet and slippery steep incline, went to duck under a dead limb, the limb snagged on the loop around his neck, and the rest you can imagine. In his case the loop was a fox snare he thought he could carry easier, but a loop is a loop. He came out of it without damage, but being alone, he was certainly fretful things wouldn't end in such a way.
I'm no fan of having dangerous tools pointing at parts of me I'd like to remain undamaged. In America's ghettos, there are folk who carry handguns in the front of their pants; a position called "felony carry". This carry position has led to a wound called the "Gangsta Vasectomy". I carry my knife and my gun well away from my vitals.