Why are some people so loud about their business?

I was on the train, and these two teenagers and their friends were literally yelling about something that happened last night. They were going on about how this person hooked up with that person and what a 'slut' he/she is, they were going on about profane things. It was just really odd to hear, and I ask, why are people so loud and verbal about details about their personal life that are just very incriminating?