Darnit, I don't like being vague and I also don't like pointing to specific people and saying "YOU! YOU SOUND CULTISH!" so I'm going to have a hard time answering this question in a satisfying way, but...

Lots of people are looking into things like nootropics/intelligence amplification, entrepreneurship, and pick-up artistry. And this is great. What gives me the creepy vibe is when they say (more on the site than at meetups) "And of course, we'll succeed at these much faster than other people have, even though they are professionals in this field, because we're Rationalists and they weren't." Anything involving the words "winning", "awesomeness", or gratuitous overuse of community identification terms like "primate" or "utility".

Trying to look for examples, I notice it is a smaller proportion of things than I originally thought and I'm probably biased toward overcounting them, which makes sense since in order to justify my belonging to a slightly creepy group I need to exaggerate my opposition to the group's creepiness.