Some of my favorites that I've written or come across...

From the BitTorrent client source, an apt comparison:

  This function is like a boat made of shit, floating on a river of shit.

From my .emacs file:

  ;; Fucking RMSmacs (by version 21.3, but after 21.1) doesn't
  ;; fucking make these fucking variables local where it fucking
  ;; should, so the c-set-style we're about to do below breaks
  ;; fucking fill-paragraph for fucking all non-c-like modes by
  ;; fucking default.  Someone desperately needs to die, and I'm
  ;; pretty sure it's not just me.

This one doesn't include swearing, but is in the same spirit. From the Audiogalaxy server, above a huge chunk of regular-expression-based string munging code:

  /*

    sah's take on all this:

    "Cursed the ground where dead thoughts live new and oddly bodied,
    and evil the mind that is held by no head. [...] For it is of old
    rumour that the soul of the devil-bought hastes not from his
    charnal clay, but fats and instructs the very worm that gnaws;
    till out of corruption horrid life springs, and the dull
    scavengers of earth wax crafty to vex it and swell monstrous to
    plague it. Great holes secretly are digged where earth's pores
    ought to suffice, and things have learnt to walk that ought to
    crawl."

    -The Necronomicon