The acronym for "This Conversation Is Over". A great and courteous way to put finality on all your text messages, conversations, etc. A great new way to get the last word!
<Jules: txt to Claire> What time do you want to meet at the restaurant tonight?
<Claire: txt to Jules> 6:30 p.m. TCIO
Jules now knows that Claire is done with this conversation and will probably be away from her phone. The conversation has been given finality.
This Conversation Is Over, also pronounced as Tee-see-yo. Used to let homothugs and Joes alike know that you are in control of an argument and are declaring it over.
Joe or huge homothug: why are you so mean to me?
Alpha Male: Because you are a mad gay, TCIO!!!