Dreaving is the act of driving sloppily while intoxicated. It's not just drinking and driving; dreaving refers to the driving act itself, usually involving drifting over yellow lines, weaving in and out of lanes, sliding through red lights, etc. In order to constitute true dreaving, the driving needs to be so bad that it is quite apparent to an outside observer that the driver is intoxicated.
"-Man, that guy is dreaving all over the place!
-I know, he just drifted into the median!"