"Well ya see, Norm, it's like this. A herd of buffalo can only move as fast as the
slowest buffalo. And when the herd is hunted, it is the slowest and weakest
ones at the back that are killed first. This natural selection is good for the herd
as a whole, because the general speed and health of the whole group keeps
improving by the regular killing of the weakest members. In much the same way,
the human brain can only operate as fast as the slowest brain cells. Excessive
intake of alcohol, as we know, kills brain cells. But naturally, it attacks the
slowest and weakest brain cells first. In this way, regular consumption of beer
eliminates the weaker brain cells, making the brain a faster and more efficient
machine! That's why you always feel smarter after a few beers."
- Cliff Clavin, Cheers

There are also a lot more great quotes available here:
The Common Connoisseur | Drinking Quotes