private
Explanation
This comic plays on the double meaning of the word "privates."
In the first panel, a woman (possibly a detective or investigator) arrives at someone's door and says something like: "Hello Mrs. Hudson, I'm a bit embarrassed, but I thought you should know I believe your daughter/son has found your... private... you know... possessions."
The person at the door reacts with shock: "What?!"
The lower panel, labeled "Earlier," shows the backstory: a teacher telling students about history, mentioning "sex and the Barbie look" or something similar, while a child then asks "Then how come I'm not a coward?!" The joke connects to the word "Private" being used both as a military rank and as a euphemism for private body parts.
The humor mechanism is a classic SMBC double-entendre setup. The comic creates an embarrassing situation by having a character discover someone's "privates" -- the audience initially assumes the sexual/anatomical meaning, but the flashback reveals the actual context was likely about military ranks or something similarly innocent. Alternatively, the word "private" is being used in one sense while being misunderstood in another, creating comedic confusion between adults who assume the worst and children who mean something entirely different. The comic exploits the awkwardness that arises when innocent words have embarrassing secondary meanings.