My favorite Mencken piece is his hilarous evisceration of the chiropractic trade. He kills'em!
My favorite Mencken one-liner, which I have had on my frigidare for fifteen years or so is: "Self-respect is the secure feeling that no one, as yet, is suspicious."
If memory serves, I believe ol' H.L. couldn't come to understand how we could side with Britain in the two great wars of the 20th century. He thought the Kaiser and Hitler were just two misunderstood dudes.