Learn English – the origin of the phrase “Too busy chopping wood to sharpen the axe”

The rhetorical, as opposed to etymological, origin is the device known as paralpsis, paraleipsis, paralepsis, (also praeteritio) meaning pretended omission for rhetorical effect, because in saying we won't mention X, of course we just did.

Edit (by FumbleFingers): A later question on the same topic gives the relevant word as apophasis. It's a little hard to see from this graph, but what it shows is that until recently, the combined total written instances for various spellings paralpsis, paraleipsis, paralepsis dwarfed those of apophasis. But the graph from 1970 on shows apophasis is now overwhelmingly more common. I don't think this means the correct term for this rhetorical device has just changed - it's just that the theological use of apophatic has led to it being more commonly known, and used "metaphorically".

From the World of Worldcraft wiki:

PST is an acronym for Please Send Tell. It originated from older online games, MUDs, and MMORPGs such as EverQuest, which used [the command] /tell to send private messages to other play[er]s.