WHAT IS THE MOST UNIQUE SONG THAT YOU HAVE EVER HEARD?

That would be “Horsey Horsey”, by Buzzard Bait.

https://youtu.be/n5p5Iei-hTo

Captain Beefheart needs to be on this list, I'll go with ;Old Fart at Play; from Trout Mask:

https://www.youtube.com/watch?v=pHjOuS-rABU

I'd add:

Nights in White Satin, Moody Blues?  (Didn't see it, but this thread is three pp. long)

Black Diamond Bay,  Bob Dylan

Man on the Moon; E Bow the Letter, REM

+1 to those mentioning Captain Beefheart, specifically Trout Mask Replica.

The Blimp is another great one from that album:

https://www.youtube.com/watch?v=MpA4XpnnI_U

Unique can be taken in multiple ways.

Thinking through my albums I think one of the most unique songs is Ning Feng’s The Last Rose of Summer on his Solo album. It’s a mind-blowing difficult solo piece that I also find to be almost "easy listening" which often isn’t the case for music that is so technical.

One of my absolute favorite classical pieces is Liszt: Schwanengesang, S560 - Serenade that I have on a Vladimir Horowitz DG recording. When this song plays it catches my attention and I often start it over multiple times before moving on.

My first thought reading this thread was Pachelbel's Cannon...