For some reason, I doubt one of these text boxes says "Oops, guess I really should have used a condom..."

i need this

This scares me...and yet, i'm intrigued.

It's from Horihone Saizou's series, "Drainage City" -- the first story in the second volume. Both volumes are available in fan translation out there on the net.
(post #14766 is the cover of the first volume.)