She has a recurrent "stoner" character who is kind of fun himself, and so when the protagonist hires him to do security on the boyfriend's house, she doesn't expect much real security. She just really wants to keep him occupied so that he doesn't get into trouble. But he takes this security job seriously, which is funny in itself (camo uniforms, etc). And he invents a special cannon to protect the house, a potato gun. PVC pipes that shoot potatoes.
Okay, so that's fun, this stoner and his young sidekick inventing this gun. But Evanovich doesn't stop there. She spins it out-- the protagonist comes home to be almost bombarded with vegetables. And the vegetables are funny too-- not just potatoes. They also hurl a cantalope (she goes for the funny names). And there are little dropped-in lines, like the stoner shooting a "twice-baked".
There's a full scene built around this. BUT that's not all. In the end of the book, when the protagonist is under siege by the bad guys, the stoner arrives like the cavalry and shoots potatoes at them and wins and is interviewed by the local media.
Two thoughts here--
1) Figure out what will be fun for the reader and go with it-- really play it out, exploit it. If you go too far, you can always cut it back later. But have fun with the fun.
2) The climax should be unique to your story. How your protagonist conquers the bad guy or accomplishes the goal should bring in elements you've set up in your story. In this book, Stephanie has been kind of a house mother, gathering these little orphans (the stoner, the boy whose mother was kidnapped, the homeless stalker) around her and feeding and housing them. So her reward for this is that they are there to help her in the climax. What has your story set up for in the end? What is the unique way your protagonist can use what he/she has learned or gained during all that rising conflict? What allies has he gathered? What skills has she acquired? IN THE STORY... use what he/she has gained in the story, not just what he/she came into the story already having.
3) The climax should echo the type and tone of the book. That is, a comedy should have a comic climax (like the potato gun rescue). A romance should have a climax that has a romantic element (like one of the couple rescuing the other, or their new trust letting them overcome some obstacle). Don't settle just for a generic thrilling climax-- bring in the extra element that is unique to this book.
So let's talk about what is "fun" in stories. It's easy to see in a comedy, but what's fun in other types of books? Look at your own story, and tell us what type it is, and what you think the reader will find to be a lot of fun and you should expand?
Like the book I was talking about in the last post, with the hero who sings her swoony songs. Well, at least I and Murph think that's fun. So I might have him sing a song later too. I have no idea how to pull that into the plot, but what the heck. Also it's a big pain that most songs from the 20th and 21st Century can't be quoted (copyright). Fortunately he's Irish, so I can use Irish folk songs, but not the Pogues, alas. I mean, "Love You to the End" would SO fit their romance.
But anyway, I suspect the "fun" part for the readers might be his songs. As long as I don't have to write them myself, I think I can spin that out. Not sure how his singing can help save the day in the climax. Hmm. Maybe the villain is going to be on American Idol.