A dag is a colloquial term for a cigarette. Can also be used as a verb: "dagging" Originated in the NAPA Valley of Northeastern Pennsylvania, particularly in the GreenRidge neighborhood. One of the Burkes probably started it.
In poker, this term refers to making a badplay against the only one at the table who has more chips than you, thus risking your tournament life on a move that has zero or negative expected value.
"Your all-in move on the turn with second pair against the chipleader was such a dag"