The people here believe they are smart. Some are correct, others are not.
But at the end of the day, it doesn't really matter to me what people on here think of themselves and others as long they can articulate their opinions in an intelligent and reasonable manner.
Indeed, just as being right doesn't mean they are smart - but the point I'm making is that HN users cover a range of cleverness, and that self-estimation is pointless (Dunning-Kroger syndrome). Saying "only joke if you're clever" is all but identical to saying "anyone can joke".