[Grammar] the one who spoils his fun

[kadioguy]

[From the book Diary of a Wimpy Kid, by Jeff Kinney]

October, Monday

Well, it's finally October, and there are only thirty days left until Halloween. Halloween is my favorite holiday, even though Mom says I’m getting too old to go trick-or-treating anymore.

Halloween is Dad's favorite holiday, too, but for a different reason. On Halloween night, while all the other parents are handing out candy, Dad is hiding in the bushes with a big trash can full of water. And if any teenagers pass by our driveway, he drenches them.

I'm not sure Dad really understands the concept of Halloween. But I’m not gonna be the one who spoils his fun.

[Source]
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The blue text in the present simple interests me. I don't think that it means a habitual action. So what does that mean by the present simple?

 

[emsr2d2]

The present simple can be used to refer to a single action in the future.

 

[teechar]

the one who spoils his fun.

I see it as stating a factual trait about someone, in which case the present simple is justified.

 

[Tdol]

He does it every year.