DaveWatch: Countdown to Letterman's Last 'Late Show,' Day 21

Bruce Willis takes a montage-clip victory lap and Dave keeps it mellow as we hit the three-week mark

Bruce Willis on the 'Late Show with David Letterman.'

"In honor of Earth Day," David Letterman proclaimed during his opening monologue, "I'm doing tonight's show with absolutely no energy."

To paraphrase noted philosopher Homer Simpson, it was funny because it was true. Last night's episode of Late Show was a textbook example of why old-school Letterman fans have been grumbling in recent years about their hero of losing interest and going through the motions. Though he seemed in decent enough spirits, Dave's rapier wit appeared to be locked in "standby" mode for much of the evening. At least he was upfront about it.

Not that there weren't a few good laughs to be had. The Tim Tebow "breaking news" cut-in — announcing that everybody's favorite Christian QB had been both signed by a new team and immediately dropped — was a brilliantly executed piece of WTF-ery, as was the follow-up announcement of, "We now return you to Cash Crab already in progress." The surreal Koch Brothers as business-suited tumblers bit and the "Bernie Sanders: Gettin' It Done" segment made one a little sorry that Dave won't be around to do his thing when the Presidential election shit really hits the fan next year. But the dreary "Top 10 Things You Don't Want to Hear From a Receptionist" was the comedic equivalent of a gas tank running perilously close to empty, and Dave's conversations with guests Bruce Willis and Jim Gaffigan were regrettably spark-free, even if he did seem to be enjoying them.

Most of the evening's highlights were throwbacks: The footage of astronaut Buzz Aldrin working the red carpet at the Daytime Emmys in a space suit ("There's no red carpet on the moon, you know!") was just as surreal and guffaw-inducing as it was when it originally ran in 2000. And while Willis did show up in a goofy hairpiece and the same shirt that he wore during his first Letterman appearance in December 1985, the montage of the movie star's entrances (and even worse fake follicles) from some of his 60 other appearances on the show garnered significantly more yuks than anything else the actor said or did last night. (Considering that he's been one of Letterman's most reliably entertaining and off-the-wall guests over the past three decades and this is his final guest spot, it was more than a little disappointing.)  Put it this way: Let's say Willis' Striptease-promoting 1996 appearance, a brief flash of which was included in the montage, was a 10. That would make this one a four, at best.

There was one moment last night where Dave's subversive sense of humor managed to rear its prickly head, though it happened so quickly that you might have missed it. Coming out of a bumper for longtime Top 10 list sponsor Ford, the host expressed his appreciation for the automotive company's loyal sponsorship, shared his fondness for "nice, big" Ford vans — and then casually suggested to Paul Shaffer that he, the bandleader and the musicians all pile into one of said vehicles for a cross-country trip, abetted by "a big of primo weed."

Could this be what Dave really has planned for his "retirement"? Because, much like Cash Crab, that sounds like the kind of show we would totally watch.