D-Fault wears a tinfoil hat, supposedly as a defence against Claptrap assimilation. This would read well with the vacuum tubes and disc antennae applied to the head of each of the assimilated. This may also reference people who believe in aliens; some of them wear tin-foil "caps" to allegedly prevent aliens from controlling their minds.
He wears armor and bears a shield that seems to be made from the parts and shells of claptraps.
He has a fishing rod that is attached to his back with a dead fish lying on the back of the rod. When killing D-Fault, one can hear him say "I'd rather be fishing..."
His name may refer to the fact that he and his gang reside in Dividing Faults and their being the last "default" bandits not yet transformed into bandit-traps.
D-Fault is dubbed by a woman in the Italian version of the DLC, while in the English (and perhaps in any other languages) is dubbed with a masculine voice. This makes D-Fault ridiculously comical when meeting him for the first time.