I'm a non-active member of Mensa. I passed the test when I was in high school (almost 20 years ago) and the extent of my involvement ended was paying my dues and receiving the newsletter for a while. My membership has lapsed, but I could reactivate it at any time.
Should I list it on a resume? It's all the way at the bottom among some other 'extracurricular' activities. Is it pretentious or impressive or neither or both?
(Edit: Mensa is the international high-IQ society. Membership means I'm in the top 2% of IQ, for whatever small thing that is worth)