When one gives TMI, or shares information with someone who does not care to listen.
person 1:"Well did you catch a peek of his business?"
person 2:"I caught more than one 'peak'!"
person 1: "overshare!"
person 1: "so how did last night go?"
person 2: "well, it started off slow, but things got better as the night went on. we had a really great dinner. he had the steak. i had the shrimp. then dessert was amazing. we caught a taxi back to my place, and hung out for a while. he made some great coffee. we had a great discussion about the election..."
person 1: "OVERSHARE. ugh."