Sorry, but as an avid pipe smoker I have done a lot of reading on clay pipes (own several reproductions myself, and smoke them too) My findings have been that the old wives tale of taverns snapping the ends off due to "germs" is bunk; you see, they didnt know about "germs" back then.
Now I have not heard the one about 'bad luck', that would hold more water to smoke another's pipe; that would hold more water I suppose.
Most historians just fugure...."They break, what the heck."
Now, to clean (or in the old days; unclog) a clay pipe, just hold over a nice fire and burn it out (WHATCH YOUR FINGERS - HOT!!) it will come out clean as New!!
I do have a nice 80+ year old pipe that a dealer found a box of hidden in a German basement, I got one before they all sold.
While I love a good smoke from a clay pipe, i still prefer a good Briar pipe, but that would not be HC.