Conversations with My Students: Second Buttons

I've been watching a lot of videos from MEGWIN, a hilarious Japanese YouTuber who uploads videos daily of him and his buddies doing stupid things. They're quick and easy videos that don't require a whole lot of language skills to understand, but there was one that I didn't quite get.

I understood the words spoken even without the help of subtitles, but the cultural tradition he's referencing was completely unknown to me. You give your second button to someone? Or they ask for it? What?

Good thing I teach English to two Japanese boys who just graduated from high school! I asked each of them about this second button tradition.

Me: You know MEGWIN?
Mittens: Japanese comedian? Yes, I know him.
Me: Yeah so I was watching one of his videos and he had this thing about the second button on a uniform. What's that all about?
Mittens: Um... I think boys give their buttons to girls.
Me: (remembered Mittens goes to an all boys school) Ah, so you didn't give yours away. What do girls do with the button?
Mittens: I don't know, I'm not a girl.
Me: OK smarty pants. Why the second one? That's stupid, you totally ruin the look of the uniform. Giving one from your sleeve or maybe the last button wouldn't be as noticeable.
Mittens: I don't know.

Me: OK Slightly Racist Teenager. Explain this second button business.
Slightly Racist Teenager: Girls ask for buttons from guys they like, or boys give their buttons to girls they like.
Me: Why the second one?
SRT: I don't know.
Me: Did you give your second button to anyone???
SRT: Um uh eeehh... I gave it to my friend.
Me: REALLY? YOUR FRIEND? :D
SRT: Ah eeehh... yes?
Me: Uh huh, ok Slightly Racist Teenager... what do girls do with the buttons?
SRT: I don't know.
Me: You don't make like a cell phone charm out of it or put it somewhere?
SRT: I don't know.

Frustrated with the boys' answers, I asked Brohei-sensei about this as well. I realize this is not a conversation with a student but it's informative!

Me: I asked Mittens and Slightly Racist Teenager about the second button thing, but they didn't know what girls do with the buttons once they get them.
Brohei: Yeah, I don't know either.
Me: Did anyone ask for your button? You had a girlfriend in high school!
Brohei: Actually... I don't think she asked for mine! Maybe she asked for someone else's button?
Me: LOL THAT IS TERRIBLE. Why the second one?
Brohei: I think it's because it's close to your heart.
Me: AAAWWWW that's cute. Do some girls try to get as many buttons as they can? Like to brag about later? I think I'd try to collect as many as I could then make a cell phone strap!
Brohei: LOL maybe! I don't know. But it's an old tradition since a lot of uniforms have blazers and not the kind with the collar and buttons.

What uniforms on real teenage boys tend to look like.

I think it's a cute tradition! Brohei asked me if we did anything similar in America and the only thing I could think of was giving your class ring to someone. Someone tell me what the girls do with the buttons!!!