Here are some pages collecting ancient graffiti from the walls of Pompeii.
Among the ones I particularly want to remember for special occasions:
Lucrum gaudium - Profit is happiness
Myrtis bene felas - Myrtis, you do great blow jobs
And, of course:
I.4.5 (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.