I don't think no one has done this yet. But I regret losing my Nintendo DSI. What did you regret doing in the past?
In primary school, I once kicked the school bus for no apparent reason other than to show off, and that very miniscule, practically non-existent "scratch" I had caused got me and my parents in so much trouble. I do regret having done that.
Aside from that, I have a few regrets regarding projects I've worked on. Things that I should have done differently and/or that led to negative consequences for me and/or others. One of those being a student project where we prioritized the wrong things and, as a result, ended up with an unpolished product that we got scolded for, the other one being a contest where I didn't consider the rules carefully enough and as a result got disqualified. Would probably do both of these things differently nowadays.
Feel free to visit my website/blog - it's updated rarely, but it looks pretty cool!