Slang for the word "duct", as coined by famous youtuber FlightReacts in his universally panned song "Cold-Blooded" (which also rips off the hook from the Lil' Boosie song of the same name).
Dutt, anyone who is utterly and outrageously stupid..
In reality, whoever says it is the idiot.
It means that they have no other comeback or just say it because they think it sounds cool in their tiny brains where the word 'Dut' is 'cool'