D'oh! I was busy wrapping up the school year and completely missed Wacky Day! I did just vote in the poll, though, and while I don't know if I have any great wacky stories, I'll at least share my "origin" story.
During the summer of '73 my parents packed my three brothers and me into the station wagon to take a road trip from Chicago to Rhode Island to visit some family out there. I already had a small sticker collection (it seemed to be something kids in the neighborhood did, even if I don't recall any rhyme or reason to what was collected). When hanging out with my cousins, they introduced me to Wackys. I was thrilled! On the morning we packed up to head back to Chicago, we stopped at a drug store and bought a few packs. Sadly, I forgot those first packs at a hotel in Ohio on the way home. I was devastated and asked my mom if the hotel would send me the stickers when they were found in our room. Needless to say, they never made their way back to me, but not long after returning to Chicago, I found them in a local store. I suppose I assumed the first series would be the entirety of Wackys. When, some months later, some neighborhood friends showed me series two, it was love at second sight all over again. I was already a collector of things and knowing there were two series (and more on the way, I hoped), made it seem that much more fun to me. I recall my interest starting to wane a bit by series 9 or so, and I don't recall buying any after series 12, but those early series are definitely seared into my mind as one of the wonderfully fun things about childhood.