I have often seen leitzanus, mockery, defined along the lines of making a joke out of serious matters. Intuitively this is a good definition, but does anyone have a source which spells it out?
Orchos Tzadikkim, at the end of Shaar Hashtika, has a quite extensive explanation about the various types of Leitzanus. See here.
It is in Maharal: ספר נתיבות עולם ב - נתיב הליצנות - פרק ב הלצנות הוא הפך הדין כי הלצנות הוא דבר התול "... Leitzanus is the opposite of "Din" in that Leitzanus is the concept of mockery..."
(Unfortunately Chelek Beis of the relatively newer print of Maharal is not yet available)
There is other material there and in the previous perek which builds a strong case for the definition you have proposed.
Rav Hutner, in Pachad Yitzchak on Purim, Maamer Alef, explains it the way you are saying and bases much of his thesis on a statement of Rabbeinu Yona. He adds that the only Leitzanus that is ever permitted is when its purpose is to restore honor to that which it is fitting.