I don't know. Maybe this particular issue isn't as clear as I seem to think it is. Maybe I am being unreasonable. Perhaps I should break it down into understandable language.
The item circled in red below is called a turn signal stalk.

It is located to the left and behind the steering wheel in most American automobiles. Consult your car's Owner's Manual to correctly identify where your turn signal stalk is located.
When manipulated, the turn signal stalk causes the turn signals (items circled in image below) to blink. Generally, pressing down causes the left turn signals to blink; pushing up causes the right turn signals to blink. Again, consult your car's Owner's Manual for specific details.

Typically, one would want one's turn signals to blink before
a) making a turn at an intersection, or
b) changing lanes.
Doing so alerts other drivers on the road (especially anyone behind you), that you will soon change speed and/or direction, allowing them to respond accordingly and in a timely fashion. Not only is this a safety issue, it is a common courtesy.
There are no exceptions to this requirement. Perhaps I should repeat that.
There are NO EXCEPTIONS to this requirement.
Your special circumstances do not void the law. It does not matter who you are, what car you are driving, what time of day it is, how you are feeling, how late you may be, what you have eaten, or if your dear Auntie Betty just died. No exceptions. No special circumstances.
In particular, it would be wise to use your turn signal when cutting in front of a 20-year old college student trying to get to his 8AM Drama class on time, preferably without getting into a major car wreck on the way. Furthermore, you would be most fortunate if said college student is a Christian, and thus restrains himself from honking his horn while throwing out colorful phrases to describe you and your driving skills.
This public service announcement has been brought to you by TheThousand.net.

*died of laughter*
could you make a flyer out of that so i can send it to some drivers i know? ;-p
Aliotsy, AMEN TO THAT!
I ABSOLUTELY HATE DRIVERS WHO DON"T SIGNAL WHEN CHANGING LANES IN CROWDED FREEWAYS OR LOCAL ROADS. They think they are all that... cutting in front of you without using their lights when you're going 80-90 mph. I almost got into an accident coming back to davis on Mother's Day because this stupid teenager in a stupid pickup truck decided to cut in and out of the lanes without blinking. Not only did he almost have a collision with me, he almost hit other cars too. It looked like he was trying to show off his skills. Ya... some skills.