The older, more world-weary Tidus. Like father, like son. Only Jecht seems more abrasive, more self-confident, more agressive. More drunk. Though he comes to accept his faults and try to be a better person, at first he's not so easy to be around. Jecht knows he's a star blitzball player. He knows he's respected and loved by his fans. He knows he trains hard and plays hard. He won't let you forget it, either.
Underneath all that testosterone, Jecht cares deeply for his family, particularly Tidus. Of course, he has a screwy way of showing it, always verbally abusing Tidus and telling him he's not good enough. No wonder Tidus hates him. Talk about dysfunctional families.
"You were always such a stiff, but that's what I liked about you."
Auron never really warms up to Jecht. Jecht is an outsider, and as such, can't be trusted. Auron constantly berates him for his mistakes. Jecht refers to Auron as a "stick-in-the-mud" and a "stiff." The two can barely tolerate standing next to each other to appear in one of Braska's spheres.
But somehow Braska brings them together. To protect him, they would both put aside their animosity toward one another. And though Auron would never admit it, he fears losing Jecht just as much as he fears losing Braska. When Jecht and Braska choose to die to summon the Final Aeon, Auron mourns both of them--and promises to look after both of their children. For Jecht, Auron literally travels to another world to fulfill his promise. Sure, Auron is a man of his word, but would he really go to all that trouble for someone he hated? I doubt it.
Auron and Jecht have much the same relationship that Auron later forms with Tidus (which is probably why they're also a popular yaoi pairing, to which I also say yuck-o, having never been a fan of rival slash. This is so not helping my reputation as a rabid slash fangirl, is it?). They act like they can't stand each other, when it's quite obvious that underneath all that crap they're good friends who look out for each other. But shhhh, don't tell anyone!