Realizing that I have the sense of humor of a 3yo.

3yo: "The store is closed."
Me: "Whaaaaaat?!! How can iiitttt beeee closed?!"
*Zeni & 3yo crack up*
3yo the rest of the day regardless of context: "whaaaaat?! How can ittt be closed?!"
*Repeat Zeni & 3yo crack up*

It's not even developed enough to call it "juvenile humor", more about wordplay, exaggeration, and observations on the pure absurdity of reality.

Fortunately, my 3yo thinks I'm the funniest person in the world.

All bets off when he turns 4.

Sounds like you and your 3yo have a great sense of humor together! Enjoy these moments of laughter and silliness, they are truly precious. Who knows, maybe even at 4 he'll still find you the funniest person in the world. Keep the jokes coming!