In late adulthood, mr. klondike has become increasingly likely to make a socially impolite remarks about other people's appearance or mannerisms. his blunt comments are most likely to indicate late life atrophy of the lobes.

frontal

Explanation:

In a mammalian brain, there are four major lobes that are present and one of them is the frontal lobe.The frontal lobe is mainly rich in dopaminergic neurons and thus, it is mainly concerned with functions such as memory, reward, motivation, planning, attention, etc.The process of break down of tissues and cell death in the tissues is referred to as atrophy and since the frontal lobe is associated with the functions as mentioned above its atrophy would lead to a slow decline in these functions.Since Mr. Klondlike behavior is changing his blunt comments are most likely a result of atrophy of the frontal lobe.

That would be a working theory.