Certainly the three young men Geoffrey Chaucer refers to as "rioters" or "revelers" (depending on the translation) in "The Pardoner's Tale" are suffering from some serious character flaws. The two most obvious are greed and pride (arrogance), since those are the two that are most responsible for their deaths.
These young men are quite arrogant, and they are made even more so by drink. They demand to know for whom the bells were tolling and then start to boast that they will find this thief, Death, and kill him so he will stop killing so many people. When the innkeeper warns them to be careful, the young men are unfazed; they are drunk and they believe themselves to be invincible; surely Death will be no match for them.
"Yea, by God's arms!" exclaimed this roisterer,
"Is it such peril, then, this Death to meet?
I'll seek him in the road and in the street,
As I now vow to God's own noble bones!
Hear, comrades, we're of one mind, as each owns;
Let each of us hold up his hand to other
And each of us become the other's brother,
And we three will go slay this traitor Death;
He shall be slain who's stopped so many a breath,
By God's great dignity, ere it be night.
They resolve and swear to kill Death by the end of the day, a lofty goal for sure. When the rioters do find Death, they do not know it, for he is disguised as an "ancient man." He is so old-looking, in fact, that the revelers demand to know why he is not already dead. The man is humble and recognizes what kind of character these young men have, so he directs them to a great pile of gold. Of course he knows what will happen.
The three rioters are so greedy that these former friends (who just swore an oath as brothers), within a day, turn on one another. Each one of them is prepared to kill the other. That, of course, is exactly what happens. Their greed is what literally kills them, but it is their pride and arrogance (and a stunning lack of judgment) which puts them in the position to be greedy.
Perhaps one other quality the rioters represent, then is the foolishness of excessive drinking. The Pardoner, at the end of the tale, ironically condemns the young men's "gluttony, lechery, and hazardry," all things the Pardoner is guilty of in his own life.