I think Katie wrote this portion of the Comlex Review

p.176 Defense Mechanisms

4) Mature defenses-these defenses distort reality less than the other defenses and are thus considered more mature.
a) Humor-permits the overt expression of feelings and thoughts without personal discomfort
i. Example: A student smiles when he realizes that a particularly intimidating professor looks like a penguin.

See Katie- giggling everytime you think of penguins is actually very mature!