My grandmother told my cousin, a military man, that all the greatest wisdom in life came from animals. At first we thought she was talking about /r/adviceanimals, but then he received the following mysterious missive in her will...
The pictures, in order, are:
1. A herd, mob or troop of kangaroos. (Image is tagged "Kangaroos")
2. A troop or shrewdness of apes. (Image is tagged "Various Cinematic Great Apes")
3. A scourge of mosquitoes. (Image is tagged "Insectoid Vampires")
4. An army, colony or knot of frogs. (Image is tagged "Frogs")
5. A wisdom of wombats. (Image is tagged "Wombats")
added mob for kangaroos (thanks @Dan Russell) and colony/knot for frogs
Adding in the connecting words,
(Herd/Mob/Troop) (troop/shrewdness) is the scourge of (army/colony/knot) wisdom.
Selecting the most sensible sounding set of words from the alternatives:
Mob shrewdness is the scourge of army wisdom.
I think this maybe is intended to mean, roughly,
Mob mentality is the scourge of army intelligence.
Since your cousin is a military man, that sort of makes sense.
By the same principle, the title is
The unkindness of ostentation - confirmed by OP.