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

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...

Miles Davis and Gil Evans "Nothing Like You"
https://youtu.be/iwQSLtLJHYg

Siouxsie And The Banshees - Peek-A-Boo
Zappa - Calling any vegetable

Side 2 of Lou Reed's 'Metal Machine Music'.... 

Wow, not one but TWO mentions of Birthday, must say that I screamed the very same when saw the thread title. Hmm, maybe almost as unique as that (now that surely must be an oxymoron!), in second place, silver medal, runner-up...
All Tomorrow’s Parties
The vocal is odd, the organ timing is most odd, the guitar is odd and the drum is just, well, odd. And I love it so dearly for all of those reasons.