Dic: happen to be (do) something

• This happens to be my house!
• That happens to be my mother you're talking about!
• I happen to live here too!! don't leave your garbage everywhere!

■ Somebody/something happens to be something: used when telling someone something in an angry way.

■ happen to be/do something used to tell somebody something, especially when you are disagreeing with them or annoyed by what they have said.

■ happen to do sth: (3) SPOKEN. used for expressing an opinion firmly, because you are angry.

.... LDOCE, OALD, Macmillan