I would go back to when I was in high school and re-enjoy a few parties. I would also take a movie like Terminator Salvation and take it back to the 70s and tell people that was the world I came from. The graphics would make their heads explode.
I would generally just screw with people showing them ridiculous technologies we have, like laptop computers, iPhones, etc.
Then I would go back to being 18 and sleep with some other 18 year old girls... just because it would be all good.
Of course, I would get rich as hell too. I would probably go back to like, the last thursday before a massive lotto win, and win it. That way I would only be displaced by a couple weeks. Then I would throw old me into a dumpster.