Apparently graffiti hasn’t changed too much over the years, as these translated examples from Pompeii demonstrate:
(House of the Citharist; below a drawing of a man with a large nose); 2375: Amplicatus, I know that Icarus is buggering you. Salvius wrote this.
(House of the Centenary; in the latrine near the front door); 5243: “Secundus defecated here” three time on one wall.
(barracks of the Julian-Claudian gladiators; column in the peristyle); 4289: Celadus the Thracian gladiator is the delight of all the girls