I saw many random bands for the first time on Letterman back in the NBC days when he lurked at 12:30am and the musical act would pop up around 1:20am... the stoner's hour... perfect time to hook in a couple new fans. That was still at a time when a band was on for just the hell of it and not because they were solely making the TV circuit on a promotional tour to boost album sales, or the parent company owned both the TV station and the record label.
TV appearances don't mean as much today as they once were, but at least your parents are finally getting tipped off to what's hip these days. But there was once a time when a TV spot could make or break a career... or a stint on late night TV was the start of the countdown on a band's 15 minutes of fame.
Letterman is a lame duck President, ready to sail off into the sunset in a few months. Sure, he's a little jaded and tired and just biding his time until his retirement. I sense he's not easily impressed, which is why his reaction to Foxygen is priceless. Pure enthusiasm with Sam from Foxygen's outrageous Mick Jagger imitation and a Van Morrison leg kick as an exclamation mark.
I'm assuming Letterman had no clue about Foxygen other than hearing a few seconds of a song one of his interns played him. Letterman probably skipped soundcheck so his first real dose of Foxygen was the over-the-top performance with all the stops... a trio of background singers, a bunch of junkie-looking backing musicians, and a "is he gay or just really fucking weird front man?"
Broseph tipped me off to Foxygen's first performance on Letterman...