After he is resurrected, Dean burrows his first change of clothes from Bobby. That includes this long-necked grey-brown Henley. Its buttons run from collar to sternum.
Dean puts in on in Lazarus Rising (4x01), after he’s convinced Bobby that he’s not a demon or shifter, and he’s thus gained access to a shower and borrowed fresh clothes. He wears it until he and Bobby track down Sam. He changes out of it after Bobby leaves to call Pamela and Dean tells Sam that he doesn’t remember Hell.
FATE: Returned to Bobby.