I propose that the first reliable written evidence concerned a Trans-phobic Roman Emperor, suspected by his opponents of being Gay, in what has become known as the 'Bona Dia Scandal". Publius Clodius Pulcher was arrested, and may well have died in prison, for the crime of appearing dressed as a female harpist at a society event in the home of Julius Caesar (100BC-44BC). 

This post was edited by Hannah Ceridwen Eluned Cavendish-Grosvenor at March 29, 2016 3:21 PM BST

With all those toga's, how could he tell??