This expression is usually screamed, but does not necessarily have to be yelled at the specified target. Used when someone is engaging you in a story or conversation that you don't feel like hearing. When used correctly the speaker will feel embarassed, and immediately stop boring you with their story. Can be translated to "I don't care," or "Shut the hell up."
T: Yo I was in class today and my professor was telling us all about psychology.
Brett: O yea, what was he saying specifically?
T: Well he was telling us how the brain
Irv: DATS COOL!!!!
(Silence is restored)