After weeks of painstaking research, I found this little gem:
More than 10 years ago The Cactus was born. It started with a BBSer named Amigados who started pranking people and saying absolutely nothing except for “cactus” at them. He did a few Cactus pranks for RBCP who immediately stole the idea and started doing it himself. Years later the PLA began and Cactus started to get more well-known than it deserved. The Cactus prank turned up in various PLA phone calls and issues of the old zine. The next thing you know, kids start writing “cactus” all over their schools, a clueless newspaper reported that “cactusing someone” was a form of harassment and el_jefe even got the word “cactus” banned in his classroom.
“To live the cactus is to live like no man.” -Amigados, 1995
I doubt the first one was even recorded. I'm sorry, Nova.