(Acronym) "I Don't Think So." First used circa 2004 by Elizabeth Soto and friends.
In response to trying to get something for nothing: SELLERS WANT INTERNATIONAL POSTAGE FOR LOCAL RATE. "I.D.T.S."
As a threat: "I.D.T.S. pal!"
In response to a statement made by someone who is trying to kid you: "Hey man, I won the lottery today!" "I.D.T.S."