Everything you go to will be filled with people who are uninteresting to somebody, the best way to get around it is to choose something that will have a range of types. That will be able to provide a variation among people and have that variation of types be somewhat random.
take a class in some subject that is somewhat outside your comfort zone, so if you're a programmer don't take a programming class. I would recommend an art, music, or literature class. Downside, lots of uninteresting people really into those subjects can also be pretentiously annoying.
Other classes one can take that will also be healthy for you: Dance, cooking (maybe of some type that is not that well known or trendy will improve chances), Capoeira - has a generally gregarious culture and tends to have people who are not as much into the general martial arts stuff as others - especially Capoeira Angola.
However all these things probably betray my particular interests and where I might expect to find people I consider 'interesting', it's a pretty subjective quality.