Banality is that force which is slowly removing all the wonder from life, and replacing it with false promises and empty shells. Human victims of banality generally appear to be unchanged, and indeed deny that there is any difference to their personalities, instead ascribing it to maturity or some other force. However, the change is visible to most people with a modicum of perceptive ability--all the love of life has generally departed from their actions, their sense of humor disappears, and they feel a great need to puncture any and all manifestations of true creativity.
Ironically, many 'creative' people are servants of banality: their works are flat and sterile, generally look like one another, and are often _very_ depressing, to the point of nearly being suicide notes disguised as art.
Some other examples of banal people: government officials and politicians, advertising or other corporate executives, most teachers, and art/music/book/whatever critics.
Places and things can also succumb to the effects of banality: such affected places tend to look like each other, and they are generally gaudy, noisy, and have color schemes developed by behavioral psychologists to rope in as many people as possible.
Unfortunately, in these latter days of mass marketing, lies from those in high places, and endless criticism of everything from every source, banality is slowly but surely gaining the upper hand in human thought and behavior.