Straight to the point, Yusuke Urameshi is a funbag full of flaws. He isn't your average shonen hero, with their naivety and faith in friendship and trust. He's a smart-mouthed, street-wise brat, who doesn't take no for an answer and flips off authority in it's face when he can. He's brash, loud, crude, impatient, reckless and violent, all with a hot-headed temper and a cocky ego to round it all out. He's more the type to try to fix a problem with his fist instead of his head (although headbutting usually helps in a pinch), and his morals are gray at best. In fact, his approach to rules was the very reason why he was hired to become a Spirit Detective in the first place, as the last man with the job had gone insane because he was too rigidly black and white instead. He's lazy and absolutely hates to be bossed around, constantly griping about cases Koenma gives him until Botan bribes or beats him up to do it. He's also painfully honest and has a sharp, sarcastic tongue, so if he thinks something is stupid, he will be the first to let you know. And make fun of you for it. Extensively. Yusuke's kind of a huge dick when he wants to be. He can be a stubborn brat when he's pushed enough, shoving aside maturity in favor for what he wants to do, and striking out on his own if he gets angry enough, like plotting with Hiei to overthrow the Tournament when things got bad, or refusing to look for Kuwabara when he went missing because of an earlier argument.

However, despite ALL OF THAT, he's actually a good guy once you get to know him, and it's not really that hard to see once you get past his Mr. Tough Guy exterior. Deep down inside, he has a heart of gold and a good sense for what's wrong and what's right, ignoring the labels of good and evil (or rather, human and demon) and deciding what's best for everyone. A lot of his bad behavior and anger most likely stems from a neglectful childhood with an alcoholic mother, and a general anti-social attitude, refusing to trust others around him with his problems and shouldering most of his burdens on his own. He had, initially in the series, been very bitter and jaded, even wanting to stay dead because he figured nobody else liked him and his mother would be happier off. Of course, once THAT had been disproved by watching his own wake, and spending most of his trials helping others, he returns to life with a stronger outlook of things, and a deeper appreciation for his friends.

This only grows stronger throughout the series, as he becomes rather protective of the people he gets close to. Keiko, naturally, is a HUGE example of this, as he literally risks his life a number of times to make sure she isn't hurt. He also emotionally breaks down after Genkai and Kuwabara were killed in front of him, hating himself for not being stronger to protect them. Also, like other shonen protagonists, Yusuke has a sort of charisma that attracts people to his side (Hiei being a significant example), getting even demonic kings bent on domination (hi Yomi) to enjoy a good spar with him. He can have an almost childlike enthusiasm in the odd occasions he gets excited for something (like his fight with Jin), and he strangely enough gets along well with children, perhaps because he's something of a huge kid himself.

On the subject of fighting, Yusuke/Fighting is a canon OTP and EVERYONE KNOWS IT. It doesn't matter if it's a friendly sparring match, a scuffle between a rival, or an epic life-or-death brawl; if it involves duking it out with someone, he'll be there. As Genkai quotes in the dub, "If Yusuke wasn't in constant danger, he'd die of boredom". The more thrilling and dangerous the match, the better, as he is one hell of a battle junkie, and he'll do anything to get a fix. Part of his reason to go to the Demon World later on in the series, actually, was because of this constant urge to fight, feeling as if he didn't belong back in the Human World because of it. While fight-happy, he doesn't discriminate between opponents very much (during the Yukina arc, he had no issues going against seemingly female fighter, because "she's a fighter and she wants to fight!"), though he won't pick a fight someone who's drastically weaker than him, unless they piss him off to the point where they really ask for it. He also has an aversion to killing others, if he can help it (canon fodder demons don't count), not wanting to end another person's life in the chance that they may fight again on better terms