The Bruce Willis movie about it did pretty well, though.
True, I suppose it would be a good at calibrating for uselessness. 
You forgot that BSA motorcycle parts were almost exclusively made from Unobtanium, although the parts that weren’t were always lost ‘somewhere in shipping’ (the on-the-boat syndrome).
IIRC, ytterbium is used as a dopant in optical fibres. It can amplify light propagating through the fibre and AFAIK there are even lasers built in Ytterbium-doped fibres. I think such fibres are available commercially nowadays.
All of the elements are equally useless. Perhaps the question is: What is the least useful element?
The answer would be Nitpickium
IIRC, Isaac Asimov described molybdenum as the worst element. Or at least one of his characters did. It was mostly the name he was objecting to, but does it have any actual use?
Moly grease is a popular automotive lubricant. Indeed pure molybdenum disulfide has lube applications too.
Alloyed with other elements and iron to make bicycle frames. Race car tubular frames, too iirc.
I didn’t know about scandium and handguns, but it has been used (still is?) to make bike frames.
Mo-99 decays into Technetium-99m, which can be mixed for a variety of different medical diagnostic uses.
How about high-strength steel?
Along with the bucket of sake, guilty of posting whilst not fully aware.
There needs to be a hanging head in shame smilley
Hafnium’s used in plasma cutter electrodes. cite: Facts, pictures, stories about the element Hafnium in the Periodic Table
My cite is a cool site, BTW, if you’re interested in seeing pictures of samples of as many elements as possible.
Believe it or not, molybdenum is a cofactor for several important enzymes, such as xanthine oxidase. It is thus a required nutrient and it is possible, although very rare, for a patient on long-term parenteral nutrition to develop a deficiency if not supplemented.
And you use a cow to get the Tc!
moo
Not just 1 cow, 99 cows!
Yep, it is the Y in YAG lasers:
I’m told that the tube on my argon laser is made of beryllium.
That’s yttrium actually. Similar physical and chemical properties though.
Thulium. Element experts Theodore Gray (American) and John Emsley (British) attended a conference that was aired and both agreed that Thulium isn’t used in any way by plants or animals, it serves no industrial purpose of any value at all and it’s a lanthanide nobody wants or needs. It takes up space on the chart of elements and that is its only value.
Curtis Stotlar
Irradiate in a reactor and the decay product produces X-rays. Useful for doctors and dentist who have no access to electrical power in the field.
One character in an Asimov story hated praseodymium, atomic number 59, because it is the only element with six syllables in its name. The character, a (fictionally) famous organic chemist, heartily disliked words with unnecessarily many syllables.
Praseodymium, however, appears to be quite useful.