Genesis 4:23

And Lamech said unto his wives, Adah and Zillah, Hear my voice; ye wives of Lamech, hearken unto my speech: for I have slain a man to my wounding, and a young man to my hurt.

1. Lamech told his wives, Adah and Zillah, that he had killed a young man.
2. Lamech was apparently concerned about the consequences of his killing of a young man.
3. Lamech's manner of speaking makes this seem like a very formal occasion - I don't know whether that was true or not.
4. Lamech did not attempt to conceal what he had done from his wives.