It's interesting to see what people consider childish behavior, but that's fine by me!
I can't think of anything that wasn't named here. I thought I would be the only one making pencils fight with sound effects (I also like to turn on some kind of fitting battle OST on youtube), but it seems like there are others with similar tendencies.
When nobody is at home, I also like doing fight moves and pretend like I am destroying a robber that is trying to steal my stuff, but I am glad that I am not the only one.
The only things that I didn't see mentioned here is that I kind of sort of still have an imaginary friend that I talk to when no one is around. I am not sure if you could call that an imaginary friend since I am talking to myself (and am aware of that..), but its fun to act like you have two conflicting personalities ('fun' might be the wrong term to use here).
I am also really scared of large gatherings, which is why I was never at a party and mostly sit at home. I was actually feeling pretty proud of myself when I went out with a group of friends to the movies. It was awkward and i don't know if it was a good decision, but it was a fun experience!
Oh, and I hate driving (is that childish?). I am also very easily scared (afraid of cockroaches, driving, heat/fire and some other stuff).
OH, I thought of the worst one! I cry really easily. If someone screams at me, its just tear-inducing even though I am not really scared of the person screaming or disappointed of myself. Its just a reflex that I got somehow.
(Almost 19 years old and still getting teary eyes from being screamed at or under stress.. Very embarrassing.. No wonder I have never had a girlfriend.. Oh wait, that's a childish thing to say, excuuuse me)