A tragic flaw is a personality trait that leads to a character's downfall. There are many such examples in Sophocles's Theban plays, as there are in Greek tragedy in general. Tragic flaws are normally given to heroes, but by no means exclusively. In Antigone, for example, the relevant leader is Creon, and he hardly fits the traditional mold of a classic hero. His character flaw is a common one in Greek tragedy, and one shared by all the leaders in the Theban plays: hubris, or overweening pride. Creon has made the fateful decision to defy the gods in refusing to allow Polynices's body to be buried according to traditional rites. He stubbornly refuses to listen to advice and continues to insist on his word being obeyed without question. Creon's hubris leads directly, not just to his own downfall, but to the deaths of his wife and son.
In Oedipus Rex the title character is also undone by hubris. Oedipus shows pride in defying fate as expressed in the prophecy of the Delphic Oracle. In fleeing Corinth he's trying to escape his fate. But try as he might, he cannot. He has taken into his own mortal hands the decision of the gods and so nemesis cannot be far away.
In Oedipus at Colonus Oedipus is a good deal wiser than in the previous play. Yet there are still more than a few traces of residual hubris in the old man's personality. For one thing, though outwardly more pious, he starts the play by knowingly trespassing on sacred land, and what could be a better example of hubris than sitting upon ground forbidden to mortals?
Oedipus also shows his pride by refusing to accept that he's in any way responsible for what happened to him at Thebes. This flatly contradicts his attitude at the end of Oedipus Rex. Oedipus also bears extraordinary resentment towards his sons for not preventing his exile.