As some of my friends could tell you, I used to laugh a lot. All the time, over nothing. Largely in the breaks of conversations, when something would strike me funny, and I'd laugh out loud. At sleepovers I would bite my fist late at night in an attempt not to burst out at the memories of a recently read Garfield.
Those who knew me best just didn't bother asking what I thought was funny any more. They would hardly pause, because usually what stuck me was something not particularily interesting, witty, or even, well, funny. Just something dumb. But when I did want to share something it was annoying because I'd chuckle to myself and nobody would even turn their head.
I don't really do that any more. But as I was going down the row planting strawberries (a job, by the way, which I have now finished) I realized I was grinning madly away to myself. Picture me with a smile like that of a chesire cat. And I think I still do that at least as often. Often it will be over a quirk in human nature, or a specific human's nature, that I find amusing. Some small memory or recollection.
And there I'll sit grinning madly away to myself.