You're right, “only I matter” and “only I and [subgroup] matter” are not nihilistic either, but that's that's not what this meme is implying or what I'm rejecting. A truly nihilistic stance is "I don't matter, no one matters, nothing matters, and there's no reason to create meaning because that doesn't matter either." If I ask "should I kill myself" then nihilism can not provide me a reason to survive. Earth before, Earth after, nothing changes. That's why Camus considered suicide to be the only really serious philosophical problem.

Now of course, nihilists aren't necessarily suicidal (although it's not uncommon). The nihilist philosophy tells us to reject meaning and to pursue personal pleasure and satisfaction and self actualization i.e. the Will to Power, not because that is the meaning of life, but because in a meaningless universe there's no reason to do anything else. The person who can achieve this becomes the Übermensch, able to overcome the limits of religion and reason to pursue ambition and no longer burdened by the sorrows of ordinary people.

And again, this isn't something that gives life meaning. It's a supposedly rational solution to the question "should I kill myself" i.e. the Übermensch wants to live for life itself and does not need a reason to do so or to find meaning for life to be worth living.

All of this is to say that, yes, real people believe this stuff and they should be discouraged from doing so whenever possible.