“Dummy! I asked you for a left-handed smoke shifter, not a sifter!” That would have been embarrassing!
When I was a machinist we’d send apprentices down to the tool crib for a long weight. “Hey, we gotta calibrate the scale, go ask the tool crib attendant for the long weight.” The tool crib attendant; in on the joke, would stall until the guy asked for the long weight again. Of course, he’d then be told “Haven’t you been waiting long enough?”
We called it left handed smoke bender.
When I was in Scouts it was indeed a left-handed smoke shifter, but I am led to believe this is a conflation of two earlier fool’s errands. One was simply a smoke shifter (still purely legendary, even without handedness). The other was a left-handed stove jack.
My mother worked for Grumman during WW II and was sent one day to fetch some dural putty. (Dural, being an alloy of copper and aluminum, was not puttied.)
When my brother worked for Western Electric, new folks were sometimes sent for the keys to the incoming trunk.
The only one I remember that hasn’t been presented already is ‘headlight fluid.’
I was on a ship once and the first mate sent me for a long weight. I was pretty sure it was bullshit, but I asked the chief engineer anyway. Then I went back to the mate and asked if he could use prop wash instead, or self-sealing stem bolts.
On the other hand, we had a small boat on board that the crew were calling a monomoy. I spent weeks trying to figure out what a moy was, and why that boat would have only one of them.
Common item on a farm or ranch…
From the chemistry lab, I know this as being sent for a long stand. (“Sure, just stand over there”).
I was also once sent for a tube of nail holes, but that was pretty obvious and kinda fun to do.
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When I was at Boy Scout camp one year a boy from another troop came to our campsite asking to borrow a “sky hook” and a “bacon straightener”. We just said we didn’t have one and sent him on his way. It was only later that I found out he’d been sent on a fool’s errand.
At my high school the common prank for upperclassmen to play on the incoming freshmen was to tell them to meet you by the swimming pool – the school didn’t have a swimming pool. (I didn’t learn until I was an adult that some people actually did go to high schools that had swimming pools).
As a young composing room worker, I was introduced to type lice.
Oy! I’d forgotten high school(it’s, uuhh, been a few … years)
Basement through 3rd floors made 4 levels. It was common for seniors to demand of the sophomores to see their elevator pass. There was no elevator. (freshmen were still in jr high at the time)
Mataguay Boy Scout Ranch, San Diego, where I was a counselor in Summer '66.
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It was a left-handed smokebender.
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Snipe hunts.
We had a three-story high school building, as well – originally built in 1908, and definitely no elevators. Upperclassmen demanded to see freshmen’s elevator passes (four-year high school, so the freshmen were actually there), and also sold fake elevator passes.
I think the Turbo encabulator counts…
Oh, yeah. I’d forgotten about those. A number of companies went to the expense of making films about them.
This is claimed to be the original but Chrysler and Rockwell also got into the act.
From the Motorcycle Parts Department: Power Bands
There is a canal which separates Cape Cod from mainland Massachusetts. There are two road bridges which cross the canal, and traffic on those can be absolutely brutal on summer weekends. As a joke, I’ve seen cars with stickers on them which claim to be passes to allow the car to use the Cape Cod Canal Tunnel.
There is no tunnel.
Hubby gets some questions about why the container containing the Bluetooth and Wifi cables is empty.
He just gives the person a look until the person figures it out.
Yes, this is at work. 
My ancient memory seems to recall the Mickey Mouse Club series “Spin and Marty” episode where they went on a snip hunt. Does that fools errand precede it or did Disney come up with it?
Snipe hunts go back a very long time. At least as early as the 1840s.
I’m seeing it was popularized in summer camps and by Boy Scouts. That makes sense.
Keep in mind this has only a little to do with the birds called snipe and nothing to do with Ship’s Engineers.