No doubt, often these cracks I think were hilarious would be proven otherwise if there were others around to judge them, but still.
A couple days ago I’m watching “Natural Born Killer” alone, and it’s at the point where Mickey and Mallory are having their “wedding” on the bridge. Mickey slices Mallory’s hand with the knife, and she goes “Fuuuuck you!” I say to nobody at all, “I hear the bride wrote her own vows…”. I really crack myself up sometimes.
They made a similar joke in the MST3K “Horror of Party Beach”. Except they aren’t really trying to have a wedding! Hehe.
My best joke, only one person was around to hear.
My boyfriend at the time and I left our apartment, to hear people in the apartment across the hall playing bongo drums. I said, “They’ve got Yoshis in there!” I just said it off the top of my head, but when he cracked up laughing, I reviewed the joke and decided it was actually funny. Go me.
(Referring, of course, to the fact that when you ride a Yoshi in Super Mario World, bongo drums get added to the mix of the music. Hee!)
I got the joke and you’re right–it IS funny! 
Another joke spawned by a video game, in this case, The Legend of Zelda, The Wind Waker: At some point in the game ol’ Granny will provide Link with a heart-replenishing substance called Elixir Soup. It was just me and my sister that night, when I went to get the soup, and just out of the blue said, “Elixir Soup, hmmm? I guess 'e licks 'er and she gives him the soup!” At midnight, I’ve found that even the stupidest jokes will crack you up!
Helping to put the framework in place for a new fence, and had to grab a handful of 8 inch long nails: held them between my fingers , waggled my fingers and said: “hey, fingernails!”
ahem