The gases of Hydrochloric Acid and Ammonia mixed together form Ammonium chloride. Which, among other things, is used as salmiak to make salty licorice.
I remember making this in high school, it’s the very first thing that pops in my head whenever I think of bad + bad = good. Granted, you must like salty licorice, or it’ll be bad + bad = disgusting :)