I’d been putting off writing this up, hoping to do all the necessary research first, but it’s a subject of discussion on Twitter (link), so here’s a brief outline:
The traditional explanation of συκοφάντης, whose etymology implies that it means ‘fig-revealer’, but is used to mean ‘informer, blackmailer’, seems implausible. Supposedly, some Athenians were evading taxes on stockpiled figs, and other Athenians were informing on them or extorting money by threatening to inform the tax authorities. This sounds like a post-facto ‘just-so’ story to me.
It seems much more likely that the ‘figs’ (σῦκα) in συκοφάντης are hemorrhoids, and that the blackmailers were extorting money from the pile-riven by threatening to reveal their sexual secrets. Hemorrhoids were called ‘figs’ in Greek (σῦκον) and Latin (ficus, marisca), and were also thought to be the result of anal sex. Given the gross double standard in ancient Greek and Roman attitudes towards anal (and oral) sex – basically, being a ‘top’ was admirable, a ‘bottom’ utterly contemptible – a Greek man suffering from hemorrhoids would likely have been willing to spend quite a lot to conceal the fact.
To make a proper scholarly note I will need to gather all the evidence and weigh it carefully, since much of it is later than Aristophanes, but my hypothesis seems plausible in itself – certainly better than the bootleg-fig story. A good place to start is Juvenal 2.13 and Courtney’s note thereon.