I recently saw a lengthy, scholarly article debating whether smoking is permissible on Tisha B'Av.
To me, this is akin to asking:
Whether a Jewish man's non-Jewish wife must immerse in the mikveh.
If there's a muktzeh issue when robbing a bank on Shabbos.
Or whether one must check a Big Mac's lettuce for bugs.
Smoking is assur de-oraisa according to many poskim—and harmful and foolish according to all of them. [Not to mention that flaw in middos of one whose smoke makes others physically uncomfortable].
Hashem gave us a kli to serve Him: our body. Destroying it to satisfy a base ta'ava should never be legitimized, even if it's not strictly forbidden as far as Tisha B'Av is concerned.
