This is an acronym used commonly by fans of the Scottish actor David Tennant who had portrayed the role of the Doctor in BBC's television series, "Doctor Who" from 2005-2010.

The acronym means: David Tennant is The 1 True Doctor.
Person 1: "Do you think the new doctor is any good?"

D.T fan: "No! DTiT1TD."
by WHOligan May 12, 2010
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