pee in a cup

Literally.

I went upstairs after "quiet time" today which, if we're being honest, needs to be called "room time" because there isn't much quiet. Out of habit I check the bathroom because for whatever reason that seems to be where the mystery messes appear. We have those little paper cups used for mouthwash, or just rinsing after you brush, and there is one on the counter. That's pretty normal, but as I am going to empty it in the sink and throw the cup away...

My thought process: That's weird, yellow? Where would they have gotten lemona...wait. Slight sniff test. Confirmed. My son has peed in the cup. Gross! Why?

Me: Noah, can you come here?
Noah: Uh sure I can! (all cheerful and what not like he didn't leave me a cup of pee on the counter!!!!! please.)
Me: Noah, did you go pee pee in this cup?
Noah: Uhhh, yeah.
Me: Son, why would you do that?
Noah: I don't know. pshhh. I just did that.
Me: Right, I know. But why? That is not an okay thing to do. We go in the toilet, okay? What if someone accidentally used this cup for a drink? Wouldn't that be yucky?
Noah: (taking way to long to ponder) Yeah cause that would be not good to drink potty.

LORD HELP ME.