What got me into piranhas: I have been obsessed with amazonian wildlife ever since i was a child. Everything from vegetation to tarantulas peaked my interest. I would visit my lfs about 3 times a week to check for new and exciting fish. They would normally bring in discus, an array of cichlids, and every tetra you could name (no piranha, mind you).
Piranhas were non existent in my aquatic world. No lfs sold them, I had never seen one in person or even heard of people owning them. They were almost fictitious to me.
One day I was browsing the tetra aisles and they had red belly piranhas! They NEVER had piranhas (as far as i knew) and i was there 3 days a week until BAM!; all of a sudden they were stocked over their heads with many different sizes of red bellies.
I remember the first day I saw them..sitting in the lfs, marveling at their silver/red beauty for appx an hour. I was in love.
I kept sa/ca cichlids at that time (jack dempsey, green terror, red texas, jaguar, and cons), and for about the next month I sat on my computer researching red belly piranhas and what was required for housing.
I ended up selling ALL of my cichlids after that month, went back to the lfs to buy my first shoal of red bellies. I haven't been able to go back to cichlids since discovering the vast piranha world.
To answer the question: My first piranhas were my shoal of 5 red bellies.