Duncan is the definition of a bad boy, being a crafty, cool juvenile delinquent who comes from a long line of policemen and policewomen: his dad, mom, uncle, aunt, grandma and cousins are all cops. He knows many tactics from his time spent in juvenile detention centers. He can carve a picture of a skull into a tree trunk and lift great amounts of weight (such as Owen, who is more than three times his size). He has a brooding, obnoxious, sarcastic and flirtatious personality, flirting with Heather despite his apparent dislike of her and mocking Courtney whenever she gets near him. He also gives Courtney the pet name "Princess" to tease her. Duncan loves to break rules to better suit himself, but sometimes the consequences are worse than what he intended. Duncan also loves to make fun of the other contestants and pull several pranks on them, with Harold being his main victim (later intensifying it due to a certain move Harold made in Total Drama Island). He considers himself as being "straight with people", rarely pretending to be what he isn't. As a result, he has been shown to either get along with or make fierce enemies with his fellow competitors, although it is more than often the latter.

Despite his mean attitude and demeanor, Duncan is actually a good person at heart, although he will never admit it to anyone else. Such moments displaying this side of him include finding a new bunny for his friend DJ after Geoff loses the first one, carving his and Courtney's initials on wood, and defending Lindsay after she is betrayed by Heather. Some quality time with Harold also makes him consider ending his feud with him after so long, though this does not come to fruition. As a way to express his feelings for a girl he likes, Duncan uses his knife to either carve her name or her face or protect her during challenges. In Total Drama All-Stars, being on the Heroic Hamsters starts to bring out his nicer side (which infuriates him, as it ruins his "bad boy" image) but soon "proves" he is a bad boy again by blowing up Chris's "Cottage".