There is so much to be said about the characters in Seinfeld that any analysis of their personalities or any attempt to interpret their motivations would consume decades of discussion time. Suffice it to say that the fab four are four of a kind, and those they regularly interact with on the show are not far behind in terms of eccentricity.
If introduced into the magical universe of Avatar: The Last Airbender, however, which character is likely to be blessed with which kind of bending? The decision ought to depend on their individual traits, of course, as difficult as it is to imagine them being given more power than they deserve.
Jerry Seinfeld — Air
Jerry Seinfeld cares about nothing. Literally. This doesn't mean that he doesn't have a close bond with certain people, like his parents, for instance, but in general he makes no commitments towards either friends or romantic partners.
In a rather twisted way, this aspect of his personality fulfills the basic requirements to be an Air Nomad and embrace airbending, which involves the manipulation of the "element of freedom." In fact, Jerry would have been able to achieve the Avatar State quicker than Aang, who remained bound to Katara for the longest time.
Newman — Fire
Newman is filled with hatred for the world, but it's a very specific kind of bitterness (mostly revolving around his career as a postal worker and the indignities he goes through every day he's on the job.)
These rage issues are best expressed in the form of firebending, as Zuko and Azula do, even if it's not the healthiest way to obtain stability. The fact of the matter is that the benders of this element are prone to becoming unstable, regardless of the reason behind their loss of mental balance.
Frank Costanza — Fire
Frank Costanza apparently cannot experience any feeling other than anger. Nearly all of his lines in the show are screeched, shouted, or yelled, with Estelle having to bear the brunt of his temperamental demeanor.
Channeling these uncomfortable thoughts into firebending would mean that Frank would become one of the most powerful practitioners in the world, assuming that the size of his fury is directly proportional to the flames he can generate.
J. Peterman — Air
J. Peterman is a flighty man; he rarely stops to think about his next move, which might work in the context of being an Air monk but causes severe problems when one is the head of a major publishing company.
Still, his habit of escaping on self-inflicted healing journeys to Southeast Asia strongly suggests that his core personality cannot be tied down to one thing. Peterman enjoys the liberation that comes with split-second decision-making, very much like the airbenders do.
Susan Ross — Earth
Leaving aside the unfortunate fact that she settles for someone like George Costanza, Susan Ross is a woman in complete charge of her own life. She comes from incredible wealth but has independently made a name for herself in the TV business, which only collapses after her future fiancé comes into the picture.
Susan embodies the patience facet of earthbending, in that her ability to stand her ground would help her move mountains — literally, in this case.
Elaine Benes — Fire
Elaine is a naturally antsy person; her daily life isn't complete if it's not filled by some complaint about the most meaningless trite event that only she would find exasperating. If there's one thing she possesses though, it's the "inner fire" that is said to be the true source of all firebending (also represented as chi or bodily energy).
The cold-ish average temperature of NYC might prevent her from exploring her abilities to the fullest extent, but it would also prevent her from burning out, which is an equally likely scenario.
George Steinbrenner — Air
The head of the Yankees, voiced by Larry David, is the frivolously impulsive George Steinbrenner, a man who considers the prospect of selling alcoholic chicken an actual possibility.
Then again, given his role in one of the most prestigious baseball organizations in the country, he does manage to pull it off with impeccable success. Airbending is most definitely his forte since it's evident that Steinbrenner is practically oblivious to opinions that aren't his own, showing how much he trusts his gut instincts.
George Costanza — Water
George technically would have been a firebender; he certainly has enough pent-up frustration, but his tendency to fall back in the face of conflict exemplifies the waterbending philosophy of "push and pull." He allows the world to take him wherever it wants as if he was floating on a permanent wave, refusing to choose his destiny in the belief that everything will turn out pointless anyway.
To the casual observer, this would seem like surrender, but it's actually giving in to forces much larger than oneself. Besides, everyone knows that George has a unique relationship with water, specifically swimming pools.
Helen Seinfeld — Earth
Helen is most probably the only character in the series who does not whip herself into a manic frenzy the way the others do. Her common sense is based in reality, unlike that of her husband, which has thankfully rubbed off on Jerry at least a little bit.
The notion of neutral jing in earthbending refers to "waiting and listening," two acts that are considered the most crucial in this particular elemental style. Helen is well-versed in both of them, having had to deal with Morty for several decades.
Cosmo Kramer — Water
Kramer is eternally easygoing, which means that he subscribes to the informal waterbending concept of "going with the flow," as displayed by Avatar Kuruk. Nothing fazes him, not even the prospect of financial ruin — because he will always have Jerry to fall back on, won't he?
Kramer's policy is clear: yield to the tide, or be dashed against the rocky shores of life. As such, it is easy to imagine him sitting in his hot tub forever, constantly heating and reheating the water with his bending powers.