This excludes people who tell very close friends important stories to relieve emotional stress, and rather refers to people who tell anyone they have met within five minutes every thing about themselves
girl 1: omg whats wrong?
girl 2: i... i think i might be pregnant
girl 1: SHIT omg?! what are you going to do?
girl 2: i dont know im soo unhappy my life is awful
girl 1: you have to go to a doctors
girl 2: i think i'll just wait and see if the baby goes away
girl: .... :|(classic case of diary slut)