The original Timmy Text was sent by a girl to an ex who had not responded to multiple emails and texts over the last several weeks. In a fit of desperation and patheticness she sent him a text that said "I miss you and so does Timmy". Timmy being a stuffed teddy bear he had given her. So pathetic was this action that all behavior similar to it is referred to as "being Timmy".
Friend: omg. that is SUCH Timmy Text. He needs to get a clue.