I was ten-ish years old and walking through the Rusturf tunnel when I came across a pink and green Whismur. I caught it, somewhat surprised and confused, and walked back to the Verdanturf Pokemon center, which I THINK I previously skipped.
There, I was informed that my pokemon had some kind of disease, and I didn't really understand what they were discussing - only that I most of my pokemon had been hit with some status effect called PKRS. I considered these two pieces of information, and did the only logical thing:
Reset my game and start again.