Winning the lottery. Not the winning it part specifically, but how I'd tell my parents and gf. I've always thought of how hard it would be to not tell anyone while I wait for the money to get into my account. Then I'd get my gf a beautiful ring and tell her how lucky I am that she was with me when I had nothing.
Then the fun begins. I'd throw a huge party and get everyone everything they've always wanted. I'd pay peoples mortgages and set their kids up with college funds. Then I'll take a trip around the world with my gf. We'll spend like a year or two out there just exploring the world and absorbing all the culture and beauty we could. Then we'd come back and buy our dream house. Maybe even buy just the land and hire a company to custom build it for us. As much as I talk shit about hating the city I live in, the reality is that I might stay here.
The last thing I would have planned to do with the money is find a solid broker and invest a portion of the money so that I can derive a couple hundred thousand a year in returns and live off of that while having millions in savings.