This is a criticism, not in a nasty way, but it is often levelled at people mildly disparagingly. I have a bit of curiosity about it, though, would like to explore it more. For a start, does the accuser not also take themselves seriously in some way at least? How do you quantify it, is it even an insult that stands up to logical scrutiny? Don't we all take ourselves seriously? And finally, is it even an insult, isn't it in many ways exactly what you should do in life, isn;t it a part of valueing life and yourself?
What are the downsides?