(Not to be confused with sex appeal, which is a direct result of sex drive)
A sex drive is one of a human's basic drives, often having the greatest storage capacity and often completely full of high-resolution video. It is usually hard, rather than floppy. Under normal circumstances, it boots whenever its user is turned on.
edit Sex Drive in America
The sex drive is a modern invention along with air, in the sense it doesn't exist in at least 99.99% of the population. Just prior to a sex drive, a suitably inebriated human male will call startlingly sober human females in a seemingly random haphazard fashion, proposing that they engage in pleasurable relations for the rapidly approaching morning. At first, this proposition has only the faintest hint of positive response. Eventually, the male will get to the bottom of his list, and call an old standby (aka a booty call), a woman who will always accept an invitation for naked cuddle-bunnies. Americans are known to be orgy driven as opposed to other sex drive moderate nations.
When acceptance is agreed upon, the male will hop into his vehicle post-haste, caring not for time of day (3am) or quality of proposition (quite low). The resulting travel--the sex drive--is of course purely imaginary in nature. As 4am approaches, the human male requires immediate nourishment, and will seek out Carne Asada Burritos for consumption. By this time, he realizes that his booty call will have found a suitable replacement for services, and that a trip to Las Vegas is required. Travel fare to Las Vegas is legendary for being inexpensive, and so the human male will depart immediately.
edit History of the Sex Drive
The sex drive did not exist prior to 1969, with the advent of cheap whiskey, LSD and Marvel Comics. Prior to that, Americans passed out at 3am, like any respectable population should. With the introduction of hallucinogenic stimulants into mainstream culture via tainted water supplies, however, there came about the illusion of the sex drive. Secretary of Defense Donald Rumsfeld (the Vietnam Era Rumsfeld, not modern Rumsfeld) called it "A commonality among all the men of our great nation, man." Some have remarked that the Sex Drive is a deeper quality of human life, and not a figment of our rapidly failing imagination. Do not be fooled by hippies talking about instinctive needs or wacko professors talking about evolutionary unifying human desires of reproduction. Babies are produced by storks wearing green hats, nothing more, nothing less.