It’s not taboo. It seems to me that people do it all the time. Parents discuss their children’s intelligence. Students compare their scores with each other. Everyone knows the pecking order, smarts-wise. There are even clubs that allow people who score well on intelligence tests to broadcast their scores.
Most of these kinds of comparisons are done with sideways glances. People with money who want others to know they have money will advertise it by buying expensive cars, houses and gewgaws. People with smarts who want to advertise it will join Mensa or deliberately use big words in conversation or deliberately talk about esoteric stuff at times when it isn’t really appropriate.
It’s always annoyed me when people use big words incorrectly. Sometimes you can see they found one word that is close to another word. The mistake makes sense. But other times it is clear they have no idea what the word means and are just trying to impress. That kind of behavior does just be opposite.
I don’t think it’s polite to compare penis sizes in public, either overtly or covertly. Money and intelligence are both replacements for penis size, at least among men. I see men doing these comparisons all the time. I avoid such situations, but sometimes you find yourself there with no easy way to back out.
People also call this bragging, which, of course, is unbecoming. It’s also stupid. Actions speak louder than words, I believe. A person who uses words in the place of actions is probably not at all what he or she is advertising.
In the end, I think it is merely impolite to brag, no matter what you are bragging about. It is also unwise. But it is not taboo.