Not really the biggest taboo ever, but probably the most repulsive thing I have ever witnessed is video of people eating human placenta. Almost nothing can make me dry heave. That did.
paedophilia and bestiality. anything where one party is the calling the shots and the other has little choice because of age/immaturity. bestiality is just straight up sick, that's one messed up childhood that drives you in to the arms of a domesticated animal.
<A BORDER="0" HREF="http://www.supercars.net/PitLane?displayFAQ=y"><IMG BORDER="0" SRC="pitlane/emoticons/sad.gif"></A>
I saw a movie on eFuKt of a japanese girl eating dick cheese a few weeks back. That thing with dry heave goes for me too, except for that video.