One of the things I think is fun that other people probably think is lame is to invent sentences that could make sense in a specific context, but no one has ever said them before. Usually I'll hear someone say something that's weird and I'll comment, "Wow, I bet no one has ever said that sentence before." I can't think of a good example with a backstory, but here's an example of one that I made up:
"I just jump-kicked a tiger shark."
See what I mean? It's totally awesome, and it's possible that in some context, it would make sense (although it's highly unlikely). And I can almost guarantee that no one has ever said that.
An important note here is that I'm not talking about randomly spouting off words. Saying, "I like your chocolate suitcase banana sword monkey breath lightsaber," would not count. That's just silly. You have to create a sentence that isn't just gibberish. And it's a fun game if you can think of good ones. Because then you get into funny arguments trying to convince people that a ridiculous sentence could make sense.
So go try it with your friends (or if you don't have any real friends, try it with your facebook friends). Here are some other examples I came up with:
"Well, so much for Sword-wielding Saturdays."
"If it weren't for my metal detector, I would never have spent that year in college."
"And that's why we're not allowed to bring potato guns to the driving range anymore."
"You accidentally decapitate one lousy sculpture, and everybody thinks you're a psychopath!"