Not sure about funniest, but if you’ve ever really stripped that song down to its parts, or tried to perform it (which I have), its an impeccably well written song. Melodically, lyrically, instrumentally and production wise. Most bands would sell their soul to write a song so good.
It didn’t strike me how complex it was until a few years ago. The amount of different guitar parts mixed together is amazing. It’s a shame that the Song Exploder/What Makes This Song Great/etc. series focus on Losing My Religion, when Man on the Moon is so interesting (and not quite as overplayed).
Pop Song 89 is, to me, the most cutting and enduring example of the band’s humor.
But yes, Man on the Moon has a certain attitude about it that is very similar to what we see in Warren Zevon. Silly pop culture references are thrown out as though their frivolousness is a key to a higher meaning. A feeling of bemused resignation—of a fundamentally comic view of life—pervades the entire song. The video captured this spirit very well in the closing scene at the bar.