best single moment in the history of music

Corey Feldman sings the Blues at 19:23 when he wallows the line, "momma don't you cry no mo" while hounds are a howlin.

or see

The Rasta Rosters' Raise Your Pipe For One Love Ja at 4:20 5 minutes of bong rips followed by approximately 2 minutes of coughing.

Also see

Raffi sings The Wheels On The Bus at 0:32 "Go round and round."
 
There won't ever be a single best moment, and if I was up for it I could write all day about perfect bits of great songs. But just one for now. The "Since you gone, I've been lost without a trace" bit in the song "Every Breath You Take". And the most amazing part is that it isn't actually a love song...
 
Best single moment in musical history: when our hairy apelike ancestors realized we could assemble all these noises into music.

Or, more recently: Mozart's soon to be father has an orgasm.
 
Pssh. It hasn't happened yet. When Wyld Stallyns embarks upon its most triumphant world tour, then the moment will have happened. Until then; meh.
 
The entirety of the "Chaconne" from Bach's 2nd violin partita. Arguably the single greatest piece of music ever written.
 
From the second chorus of Comfortably Numb right through to the end of the solo. No one plays the Pentatonic quite like Mr. Gilmour.