Graffiti
Graffiti
[Cueball sits on a toilet in a bathroom. The stall sidewall next to him is covered in graffiti: "you suck," "Mike sucks cock," "CUNT," "fuck," "BITCHAS," "dane was here" struck through and "dane is a fag" written under it, a crude pictogram of a penis, and various other unreadable scribbles.] [One block of graffiti is salient:] This graffiti is fleeting human contact both of us lost, but for a moment we're lost together. I wonder who you are.
I think I look for meaning in the wrong places sometimes.

The humor in this comic comes from the irony of a deep philosophical musing on the nature of individuals sharing a private space in a public place, unknown to one another and separated by time. The graffiti text is juxtaposed with more common bathroom stall scrawlings - insults, slurs, and "[Name] was here."
This comic makes use of the existential idea of "finding meaning where you look for it," a recurring theme in xkcd. The caption implies that a bathroom stall isn't a place where Randall would like to find meaning in life, so he shouldn't look for it there.
The title text parodies one of the archetypical pieces of graffiti: "For a good time, call [phone number]," which indicates that the person reachable at that number is available for prostitution, casual sex, and/or phone sex. However, 'good' has been replaced with 'intriguing,' implying that instead of sex, the writer is offering witty and insightful conversation.
There may be a reference to this comic in 1810: Chat Systems with the chat system called Wall (bathroom) .
[Cueball sits on a toilet in a bathroom. The stall sidewall next to him is covered in graffiti: "you suck," "Mike sucks cock," "CUNT," "fuck," "BITCHAS," "dane was here" struck through and "dane is a fag" written under it, a crude pictogram of a penis, and various other unreadable scribbles.] [One block of graffiti is salient:] This graffiti is fleeting human contact both of us lost, but for a moment we're lost together. I wonder who you are.
I think I look for meaning in the wrong places sometimes.
