Poker terminology. Used to describe a player who matches any bet regardless of the odds stacked against them to win the hand.
"I bet $50."
"I bet $100."
"What do you have? I have three of a kind, Aces."
"Oh. Busted straight. Thought I'd hit my three outter on the river, then I wanted to see what you had."
"What a callbox."
Comination of donk and tard. Usually used in poker, it is primarily aimed to give added emphasis to the degree of how inept a player's skill set is. Likewise, it can also be expanded to the realm of daily life to critique whenever a person does something that, for lack of a better phrase, is utterly and completely stupid.
For Poker: Wow, four people push all-in preflop in a $75 tourney and he called with 2 3 offsuit? What a donktard.
For life: She drove off from the pump with the nozzle still in the car and the fuel cap on her hood? What a donktard.