Is there a specific name for it?

Hello, i'm 15, from Estonia. Anyways, i have a question, and I do apologize for I am sure that it is in the wrong forum. I tried to look for the one that reminds a problem one of my friends has, probably millions all over the world have the same problem.
A person is unable of taking things seriously, even though he/she himself/herself knows it is VERY serious.
I'm sorry if it is a simple question, I just want to know if there is a medical-ish name for it.

[Roger Gould, M.D.]

No name for it, but it is commonly understood as a way of denying seriousness which makes the person scared or uncomfortable...it is usually resolved with age.

[Jaquta]

It's a paradoxical response.  Similar to crying when happy and laughing when sad.  Based on what the doctor wrote you could call it a defense mechanism.

I would be at the opposite end of the spectrum.  Social situations make me feel extremely threatened and vulnerable so I try and formalize events.

When I was young I was the bus monitor for our route.  I was so controlling I would need people to be properly lined up on time, etc.  Ironically, I was so extreme and stressed by the situation that I neglected to look at the bigger picture, which was to get everybody concerned onto the bus.  Needless to say, one day I forgot my sister.  Whoops!

It possibly wouldn't hurt for your friend to access some psychotherapy if it is at all available.