I've never understood this even though i grew up in a loud extended family that what most consider shouting is normal volume for them. when it comes to teens it's a form of rebelling against the older generations as a attempt to show their dominance over those around them without realizing that it just makes them look spoiled. I personally have no issue to tell other's to STFU when i'm in a public place and trying to have a conversation but they are being so loud i can't.