Someone tried that already (see the OP). Obviously the next step is a horrible prank involving crazy glue or jello (or both), and if that doesn’t work, the only humane option is an ironic slinky-related death.
Get some other toy that makes an even more obnoxious noise. Is there a Spencer’s Gifts near you?
I enjoyed the sound for about ten minutes. Then the enjoyment tapered off considerably.
I feel for you. Because I have godlike powers over the people in my life who own a Slinky, I can just tell them to knock it off and they do (I can also make them blow their noses when they’re snuffling). I know - legally adopt the coworker!
Try replacing it with Silly Putty? That’s what I use to keep my hands busy during lectures, and its quiet enough not to disturb other people.
What? It keeps me from subconscious pen-clicking, paper-tapping and desk-drumming.
This is obvious: make it straight.
I haven’t thought of that jingle for 40 years!.Thanks for bringing back childhood a memory. Ahh…Saturday morning cartoons in black and white, while the parents sleep in and I get the living room TV to myself, and I can even choose which of the 2 channels watch.
See if you can either sharpen the ends or the entire thing. I bet the 2nd time he custs his hand, he’ll stop.
Also, this method makes it look like an accident, and doesn’t require stitches.
Otherwise, I second the glue idea, and nix the plastic one. The plastic slinkys actually get MORE annoying, because the cow-orker will realize it sounds like farting.
If you do this, you must take pictures. 
Plastic slinkys sound like farting? I must’ve missed that one in my childhood… Though I don’t know… I can only recall one plastic slinky I’ve ever owned.
Yes but for adults, Everyone knows it’s dildo.
(NO nudity, but the not even close to SFW)
Perhaps I’m not supposed to ask this, but your supervisor has time to play with a slinky all day and works in a cube? This is not computing for me. Does he use something besides his hands to play with it? When I think of a job that’s done from a cube, I think of phone calls (slinkys are too noisy for that) and computer use (and you use two hands for that). So what does he do all day that doesn’t require the use of both of his hands or doesn’t require some level of quiet that he can play with a slinky?
Who said he used his hands?
The body part he uses to play with the Slinky is unspeakable!!
He dials the phone the same way.
ewwwww!!!
I’m not sure if I’m supposed to be grossed-out or intrigued. Hmm. 
Purchase a lovely cactus such as this and carefully insert it into the center of the Slinky. Then leave it on his desk to figure out.
Get to work early and stomp the fucker flat. Then leave a little note suggesting one of your other colleagues did it…
insert evil, cackling smiley here
You mean he uses a dictaphone…
…think about it, think about it!
Shellibean’s suggestion is thye one I wanted to suggest – if by “kink it” you mean tangling it up so that several coils loop through coils elsewhere on the Slinky. This doesn’t destroy the slinky, but renders it useless until unkinked. And in the process of untangling it, it frequently gets so badly damaged that it can’t be used. So you don’t actually destroy it yourself, buit arrange for it to be ruined by its owner. It’s the ideal solution all around.
Thanks for all the lovely suggestions. It hasn’t been bad lately, I guess he’s keeping himself busy with other things. It seems like he only does it when he’s on the phone now.
I’m thinking I’m gonna go with my origional Jello plan. To avoid repercussions in the event he doesn’t have a sense of humor, I’m going to buy a new slinky, Jello-ize it, then swap it with his when he leaves his desk. It will also help with the logistics since he gets to work before me and I would have a hard time doing the swap otherwise.
Pics to follow…
Make the Jello jigglers recipe. It stays firm(er) at room temperature.
oooohhh…another idea: electrify it!