(informal) Too much information, an expression indicating that someone has divulged too much personal information and made the listener/viewer uncomfortable.
He began to talk about his last trip to the underwear store. I told him, TMI!
When Chris updated his status with "just ate entirely too much. Should make for a great bm to share with someone later," I thought it was TMI.
(psychology) Transmarginal inhibition, an organism’s response to overwhelming stimuli.