The Best Day of My Life?

Have you ever used that statement: "This is the best day of my life"?
One of my friends has, I don't want to embarrass him so I'll not mention that his name is similar to mine with 'ton' added onto his surname.
You may think he used it to describe the day of his conversion; or of his wedding day; or possibly of the birth of one of his kids: But no!
Apparently a days boating & water skiing was the best day of his life!

But this got me thinking; What actually does constitute as the best day of your life, what ingredients, activities or emotions go into making such a day?

So:

What has been the best day of your life?
OR

If you could plan it out, what would the best day of your life look like?

[Feel free to be descriptive, unless its not suitable content, in which case don't even comment]