To the best of my knowledge, I coined it!
The term slipped from my fingertips during an exchange on ACW-l discussing the merits of various way to respond to or deal with spam. Some list member commented that they take spam and use it for rhetorical analysis in their composition classes, thereby taking the annoyance and making something positive of it. To this I responded that I don't usually make the effort to turn my spam into spammonade. There was more to my response, but this about covers it.
Mon Jan 19 09:37:54 CST 1998