Michael is a half-brother.

Your father went out to buy bread when you were born... A couple of years later, your mother found herself a new boyfriend and a year passed since they met and your mother decided that it was time for them to live together.

The problem was, your mom's boyfriend had an older son, who would have become your half-brother. When you moved in with them, everything was fine. You had almost no contact with Michael. But one time...

You were talking to your friend on the phone and swearing really loudly. And when Michael heard it, he came into your room and said

-If you don't stop swearing right now, I'll wash your mouth out with soap, understand me!?