mundungus: Bad-smelling tobacco. Not derived from
dung but from the Spanish
mondongo — tripe. "Cigarette smoke is one thing, but the mundungus Percy stuffs in his pipe is the quintessence of malodor!"
Proof positive that JK Rowling didn't name the
Harry Potter characters randomly, although the total effect of "Mundungus Fletcher" is a bit odd. A fletcher, after all, is a maker of arrows.
Some people in this anti-cigarette age may argue that "mundungus" is inherently redundant. After all, doesn't all tobacco smell bad? (Okay, at least after you light it...)