By a "meetup" I mean a regular, or semi-regular, event whereby a group of people with common interests meet in order to discuss things, including [but not limited to] the common interest.

These meetups come in many forms; some occur in pubs, some in meeting halls, some in coffee shops. Some feature speeches, which tend to be on the issue of the common interest, but most do not.

By attending a meetup two events running, or three events out of six, you'll tend to get to know many of the regulars, and become part of their social network.

One type of meetup that would obviously be relevant to your interests is a lesswrong one, but meetups of skeptic societies, societies associated with your particular sexual kinks/relationship preferences (poly meets, munches, rope meets, furmeets etc.), humanist meetups, etc. would all likely be useful to you.