Similar to the plague of mental health, people often point to an individual's (their own or another's) "Intelligence Quotient" as some kind of credential. Of course, such a credential is nonsense for all of the normal reasons citation-dependent arguments often are, but also a host more.
The most obvious problem with any sort of intelligence test is that it's impossible to create the test without appealing to circular reasoning. The only way to establish scientifically that your test accurately measures intelligence is to show that people who score higher on it are smarter outside of it, which means... You have to already agree on who's smarter for a wide range of samples to establish the validity of the test. And of course such a thing is impossible, because which of two people is smarter is wildly open to debate. Let alone the thought of reducing "intelligence" to a single number, that's just laughable.
There's also the fact that the whole concept of "intelligence" implied here is bogus; while I admit this objection is more arguable, the common notion that intelligence is distinct from knowledge is wrong because intelligence is just more widely applicable knowledge. This makes sense when you understand that the definition of belief is a potential inclination to action. Metaphysics and Occam's razor make an excellent case for not believing that people have inherent (not derived from nurture and past choices) differences in how well they learn.
But the concept of objectively measurable intelligence is wrong for even more reasons. Such a general credential is incredibly dangerous.
Normal credentials - like having a degree in biology - are meaningful because that's an empirical domain. It's also well-defined; it's clear what that credential is useful for. It allows you to make qualified claims about biology and have people take your word for it, provided your honesty isn't in question. That's the point of a credential.
But when someone's credential is "I have an IQ of 150", what is that even useful for? Does that mean every time they disagree with you they can just say "I'm smarter than you so you should take my word for it"? There are no limits on what that encompasses. It can't mean anything without meaning everything. If someone is "smarter" than me, I should always prefer their own judgements to my own unless I have information they don't or suspect dishonesty. It's an incredibly dangerous concept.
Also the age scaling. It's hard to find clear information on the internet but from what I've read the final "IQ" score is your raw score divided by your age... with adults counted as 18. Otherwise adults would be judged to be stupid and the inherent stupidity of age scaling would be exposed. It's shocking that anyone sees this as more than a joke. Why should we pick that arbitrary number to cap it at based on the "fact" that people you've sampled stop getting smarter at 18? That reverse-validates whatever intelligence curve exists: if the reason people stop getting smarter at 18 is because of a flaw with how they're educated, such a measure ensures we'll never find out about it by sweeping the evidence for it under the rug.