The day I turned four. (Yes, I have a good memory, and that day was a very long time ago.) It was a big party.
Good times, good times. Hadn't had much of a birthday like that ever since. Now I'm 18, and I end up feeling jealous of myself just by thinking of that day.
There was once a day when I woke up at 5, went up and bought myself some coffee and breakfeast with my hard earned money, and worked the entire day on a game dev project. Just steamrolled through a ton of tiles and textures. I felt like I had control of my life, and purpose, even though those two things are pretty much nonexistant in literal terms.
Ah, but when every moment is good, 'worst' doesn't mean anything bad.
I'd hate to live a life without anything good or bad happening to me. That sounds too much like death.
I've had a lot of good things happen. It's hard to pick a favorite. Certainly journeying up to the top of the second largest mountain in the solar system and watching the most spectacular sunset imaginable followed by a perfect view of the universe above is one the most awesome things I've ever experienced.