Of all the possible crimes of writing, wasting your readers' time is the worst.
Before you click "publish" on some post about what you ate for breakfast, is it worth considering whether what you've written is useful to humanity?
Before you tweet the contents of your darling son's diaper, is it worth considering that people might read it--and then wish they could "unread" it?
It's an admittedly quixotic pursuit to try to purge the world of time-wasting, narcissistic writing. But we should all consider the idea of spending a minute or two mulling whether what we write is actually worth being read. If it isn't, then we owe it to the world to spend time improving it until it is worth being read.
One final irony. If you merely consider this idea on a routine basis, you most likely won't waste your readers' time. And by definition you won't be a narcissist.