A basic, but effective anger management technique. If you feel the impulse to lash out, either verbally or physically, very often this impulse will have subsided by the time you have counted from one to ten in your head. This operates on the theory that your immediate reaction to an insult, annoyance or outrage is very often not the best one. Taking a short amount of time to allow the first flash of rage to subside will help you decide what reaction is appropriate. If after you have finished your count, you still feel like giving the offender a punch in the gob, there is a greater possibility that this is the only reasonable approach under the circumstances. More commonly, however, you will find that the urge to inflict violent retribution has passed, and you might even have thought up a withering retort which will leave your antagonist speechless, thus defusing a potentially explosive situation.
Of course, one potential problem with this theory is that it relies on the individual being able to remember the "count to ten" rule as a thick red mist descends upon him/her. If you have the composure the apply this rule, then your anger problems are probably not that severe in any case. If you are John Prescott, for example, then you may not remember to count to ten until you are mid-maul. At this point, counting to ten is inadvisable, as it may distract you from your attempts at freeing yourself from the ensuing brawl.
Naturally, the counting from one to ten is just a method of allowing a certain space of time to pass. If you are more comfortable counting from ten to one, by all means do. You can count from one to a in hexadecimal if it makes you happy.