There is this rare book, Secret Fighting Arts of the World by John F. Gilbey, in which he deatails his quest to find rare fighting arts. In one encounter, he found a guy who's art was his ability to make his breath stink like a city dump - at will - and so bad as to knock one out. The author goes on to talk of the guy's diet for this at-will breath. He relates how that one moment the guy's breath was normal. In the next, at will, it was so bad, he actually passed out.
I know some will joke about people they know with bad breath, but, though pundits without any research into mind over body arts, will knock it, it's logical this art can really be developed. Here is a link to that book by the way:
http://www.amazon.com/dp/0804816085?...E7FYXR1NC9DCN&