I use those for my pasta.
Grapefruit knife. Neither the curved blade side nor the parallel blade side are really suitable for any other job, although it works perfectly for grapefruit. I’ve tried to use the curved side to peel other fruit, but it just makes a mess.
Also makes a great dough docker.
A grapefruit SPOON might seem single-purposed to most people, but we quilt makers know better. They are invaluable when you are pin-basting a quilt, it helps make short work of closing sometimes hundreds of safety pins. 
Nothing has just one use.
Torture implement. Get your victim’s thumb in there and they’ll sing like canaries (between squealing like a pig).
The thumbnail gets in the way too much. Remove it first.
http://www.tamalespreader.com/Tamale-Masa.html
Only one use in my kitchen.
Codpiece?
With which kitchen implement?
Just remembered I have rosette irons in the pantry. Though I suppose they would work as drawer pulls if needed.
Or maybe pressing patterns into sugar cookies.
Vice grips.
garlic press
Been trying to come up with a good one. Even a potato ricer has multiple uses.
Best I can think of right now is a pie bird. Used to vent steam from pies, and that’s its only use as far as I can tell. I don’t think it’s fair counting different types of pies as different uses.
You’re missing out if you don’t see the great potential of using pie birds as toothpick holders.
Rolling pins can be used for home defense!
I am surprised it hasn’t been mentioned, yet, but…
There is always the ladle…
Can be used as a musical instrument.
And the banana slicer, which has some of the greatest Amazon reviews.
We actually have champagne openers, which seems to be useful for nothing else. (Well OK, it’s good for Champagne and sparkling wine.)
OMG I was having a crappy day but this is making it much better:
“What can I say about the 571B Banana Slicer that hasn’t already been said about the wheel, penicillin, or the iPhone…”
“I would rate this product as just okay. It’s kind of cheaply made. But it works better than the hammer I’ve been using to slice my bananas.”
“I only speak Spanish. Will it work on platanos?”
“Maybe I’m doing it wrong, but I can’t get this thing hooked up to my wifi network. Am I supposed to slice my bananas over an ethernet cable? What is this, 2005?”