Hung Out or Hang Out
The phrase is commonly used today, and not just in casual settings. It’s become so inculcated into our culture that one can use it, even in an executive board room, and no eyebrows will be raised in response.
So what’s the source of “hang out”? Although there’s evidence that the term was used as early as the 1830s to mean “loiter or idle about,” the current use of the phrase probably has a more recent incarnation.
In this context, the phrase comes probably is a derivative of speech peculiar to the 1960s hippie generation. These were teenagers and young adults who rejected “the establishment,” and developed their own particular ways of dressing, in music, and in language.
The point of much of their success was apparently how annoyed or upset adults would become by the behavior. They were easily upset by how slang affects the English language they used, and they wanted their kids to conform to societal norms.
So hippies or pseudo hippies (kids who still lived at home, but who admired the dress and lifestyle of the hippie generation) went to great lengths to avoid formality in any aspect of life. Being yourself, playing your own kind of music, or doing much of what the parents would consider inappropriate was termed “letting it all hang out.”
The current phrase, “hang out,” is probably derived from the hippies of several generations ago.
Read more at http://grammar.yourdictionary.com/slang/how-slang-affects-the-english-language.html#eufRr8YV5zwqOTqO.99