My opinion of Mensa was formed by someone who told me about how, when she was a hiring manager, she once had an applicant who made a point of belonging to Mensa and didn't seem to have anything else she was proud of or had accomplished.

That doesn't mean I am necessarily on board with the fashionable view that IQ is meaningless, but I think to the extent there are people whose IQ is disconnected from their abilities/achievements, it's going to be the ones who are preoccupied with it. So I would think belonging to a high-IQ society would send the wrong message.

Hiring managers should also be aware that in the United States, Supreme Court precedent makes the use of general intelligence tests for hiring legally fraught because they can produce racially-biased outcomes.

Definitely comes off as douchy. I wouldn't discount someone for it but it would definitely make me wary of them (probably a know-it-all who doesn't listen to other people and always knows best).