Should I wait at the bar and sober up for an hour or two before I drive?
That depends. If you had completely finished absorbing alcohol into your blood, your liver would be metabolizing it, and your blood alcohol content would be decreasing. However, every person is different and people commonly metabolize about .015-.02 per hour. However, those number can vary greatly between people. It is nearly impossible for any person to know their precise BAC after drinking. It is also difficult to gauge the rate of absorption after consuming a beverage, absent chemical testing. While a person may metabolize a standard drink, or maybe two of then in that time span, the total number of drinks consumed, the period of time they were consumed in, any stomach contents, and numerous other factors come into play.
I waited A couple hours after I quit drinking before I drove, I don't understand how I still had such a high blood alcohol Content?
As the above answer showed, people vary greatly between absorption and metabolism of alcohol.
Drinking Coffee should sober me up after I consume alcohol, right?
Coffee, with caffeine is a stimulant. It can can stimulate a person and make them seem more awake. It does not assist with the metabolism of alcohol. It does not "sober" a person up. It may mask or counter act some of the depressant effects of alcohol, but it that is all.
I drank a bunch of water before I drove, that should have helped me sober up?
On a microcosmic level it may help saturate the system, increase the water content of the body, and help facilitate a passing of alcohol in the urine and/or sweat. Alcohol is hydrophilic, meaning it is attracted to water, so it may even help delay absorption of alcohol by mixing with it in the stomach and slowing, or diluting it prior to reaching the small intestine. A second theory is that adding water, or anything else in quantity to a stomach that already has alcohol inside of it, will cause the alcohol to pass, or be forced more rapidly through the pyloric valve and into the small intestine, where a majority of alcohol is absorbed into the blood stream.
So how does alcohol reach my blood stream?
It is fist swallowed, down the esophagus, and enters the stomach. A percentage or portion of the alcohol is actually absorbed through the stomach, and into the blood. However, a majority of the alcohol passes through the pyloric valve near the base of the stomach, and enters the small intestine. Due to the large surface areas of the small intestine, it is the location where a majority of the absorption of the alcohol takes place. After the stomach it moves into the portal, or hepatic vein, and travels to the liver, where a majority of the enzymes responsible for breaking down the alcohol, or metabolizing it, are at.
So how do I know if I am safe to drive an automobile after drinking?
A chemical test, or error on the side of caution and wait much longer than the science says an average person would need to wait.