Those have...at least a tendency to have...things like word bubbles written on the mirror, saying "I eat cocks" or whatever. Not as clever, doesn't work as well as it would in a society that read graffiti aloud; but same rough principle.

Well, I've seen things like the mirror-dialogue and "He who writes upon these walls . . ."; they're endemic to high schools. I'm just a lot more impressed by the Pompeiian graffiti. Pulling in the listeners and the passers-by is new to me.

(The part of me that is still fourteen would also like to point out the greater range of meanings in the phrase "May bears eat me" that has evolved over the last decades.)

(Is true I don't think the Roman graffitist even thought of that.)