Another lapsed Mensan here. I hadn’t done much with them lately, so I didn’t bother to renew. Here are a few random observations.
I too have found that few Mensans brag about it to non-Ms. I met both charming people and tedious people in the organization, some very interesting, some rather dull. I did not perceive an elitist atmosphere. You’re guaranteed to learn something new and hear a few clever puns at any of the gatherings. Games nights are fun. Picnics are fun. I never went to any of the major regional gatherings, so I don’t know about those, but I imagine they’d be a lot of fun.
I joined 7-8 years ago because at the time I was working in an office where stupidity defined the corporate culture, and I wanted to be in some social settings where there were some smart people, and you weren’t pressured to act dumb.