Got my main frozen by submitting a 9998 score in make some noise in 3 seconds. (Really regret that one)
Was using an autotyper while restocking and when chatting on rs boards, I would have messages with like "I really L9898ve where Y9898u t98989898k h12222s restock" and crap like that. People where oblivious back then and believed me when I laughed it off as a joke.
My biggest regret on Neopets... is playing Neopets. It sort of, kind of screwed up my life a little.
I had no self-control back then.
But seriously though, there was this one time where I wasn't paying attention and accidentally donated a bunch of really, really expensive, legit bd items to the money tree through the Quick Stock. I'm such a genius.