I want to make a crab happy, what music is best for this?
Crabs keep track of all the blocks they've heard, and they will give you better bonuses for playing a block that hasn't been heard as recently. This achievement is specifically for playing the music block that the crab has heard least recently.
There's no way to know what block they have heard least recently, although it's probably a safe bet it's fairly rare. Therefore, this achievement is pretty much luck based, although you can bias it in your favor by using rare music blocks.
"GNG" and "SB-1" are the rarest blocks, as they were created by the devs as a reward (The GNG block for being a beta tester, and SB-1 for... who knows :) although there are enough of them in circulation (and enough people have them specifically for getting this achievement) that sometimes it will be a rare one of the common blocks instead. You can generally gauge how rare a block is by how much they sell for at the auction.