Its just a guy living his life so nothing against him, but building a self image around how smart you are is so cringe, and then for him to agree to be interviewed about it?

I suppose this shows wisdom isnt directly correlated with mental aptitude.

i don't understand, or at least it does not make sense, how IQ is cringe but other human innate attributes such as height or strength are not. bragging about one's bench press is accepted but not IQ?

It's because there is a strong perception (at least in American culture) that g (or more specifically our best metric of it, IQ) should translate into accomplishment, productivity, or usefulness of some kind before you are allowed to brag about it. In my experience, most people report feeling a kind of disappointment or wastefulness when high-IQ people don't accomplish anything notable, so someone bragging about their IQ in a vacuum feels cringey.

I just learned I am in the 99.9th percentile of the population from the article (I’m also 150), and I’m living proof that IQ doesn’t automatically bring success after success at all. You can totally waste your life away in HN and internet. I’m resolving to not visit HN ever again right now.

Well, you just learnt something about yourself from a HN article which pushed you towards a new resolution so it can't be a waste after all..