Why was the movie called Sideways?

Being drunk makes you see things sideways...
That's what I always thought, at least.

Apparently, in the book, Sideways is explained as a slang term for being drunk.
In the movie script, they made no mention or explanation of it.

I thought it was because wine bottles are often stored sideways.

Although there have been attempts to remove wine from the bottle in other ways, the traditional method, using gravity, has always won out as the easiest, most efficient, and requiring the least extra equipment. The best way to use gravity on a wine bottle may surprise the beer can aficionado, who will know instinctively about the hole in the bottom of the can method. Apparently, among wine connoisseurs, a simple tipping of the bottle to a horizontal position, when adequately controlled for potential spillage by putting a vessel with which to catch the resulting flow, is considered the best method.