Let's not forget we're still talking about a television show where a lot is done for the purpose of drama and sensation. It can have a sense of realism to it without being strictly true and authentic.
I do agree with beaker
, though, because I've seen it firsthand friends talking to each other in what someone else not familiar with them would think is totally inappropriate language. A good film example of what I've seen can be found in Gran Torino
in how Clint Eastwood's character relates to his barber.