The Buckleys were not old-money New England WASPs, but rather parvenu Irish Catholic upstarts. I always attributed Buckley's ridiculous verbal tics and mannerisms to a pretentious attempt at social climbing.

I think you nailed it.

Even more than the accent was the incredibly annoying habit of always leaning back in his chair, presumably to affect a lordly insouciance. It might have worked in person, but on TV it was totally inconsiderate of the viewer, who in closeups was forced to endure the vision of Buckley's grinning visage tilted at a vertigo-inducing 45 degrees.

See, I can use polysyllabic words, too.

I once subscribed to the National Review and once read a letter to the editor in which the writer asked about his 'slouching' on TV. He had even drawn a stick figure drawn in a circle to show that as the show progressed Buckley would slouch further, and further, until he was almost completely reclined. The witer stated he could tell the time by the level of the slouch, and asked Buckley about it.

I remember the response was something about his back, and a little 'urbane' testiness about thanking the letter writer for pointing this out.