The full text of this quotation is oh, so he's not just a dog bottom...he's a stoner too! and it was uttered by claudeSF at a Mountain View dinner party sometime in the late summer of 1999. It referred to a now-ex-member of #gaysf (he's been banned for attempting multiple hostile takeovers), a bestiality enthusiast who went by the nick K9boy21SF.
After meeting K9boy21SF, claudeSF spoke the line sotto voce to Decay- and myself in the absolutely arched-eyebrow-deadpan-delivery manner that only claudeSF can do. Referring to the absurdity of being worried about being perceived as a stoner when you take doggie dick up the ass, the expression is now used on the channel to mean "you have larger issues that you need to worry about"