None of the characters in Seinfeld, at least the ones who take up most of the screentime, have any right to call themselves perfect people. To be fair, they don't even try to do so, but the fact that they really don't care about the consequences of their actions suggests that they are apathetic in all instances that do not revolve around them, specifically.
Of the many shenanigans that take place in the show, there have been times when they should have not only been arrested, but sentenced to time in prison. In fact, they do receive their just deserts in the final episode, where they spend one year in jail for breaking the "Good Samaritan Law" in Latham, Massachusetts. It still doesn't forgive them for their past crimes, though.
Kramer Burning Down The Ross Cabin
Kramer gets a secondhand gift of cigars from George, who had originally received it from Susan Ross' father. He then travels to the Ross' Cabin, reaching there long before Jerry, Elaine, George, and Susan, where he shamelessly lights up his beloved Cuban and smokes it all over the obviously flammable cabin.
If that isn't bad enough, Kramer later rushes to take a late night dip in the lake nearby, but conveniently forgets the lit cigar on the mantel. It inevitably falls onto a stack of newspapers, and subsequently burns the whole place to cinders. Arson, as far as the law is concerned, is a serious offense.
Elaine And The Dognapping
Newman and Kramer convince Elaine that the only solution to her barking dog problem would be to abduct the poor mutt and abandon it far away, which she hesitantly agrees to (if only to protect her sense of stability after several days of poor sleep.)
They are obviously caught and taken to the police station when the dog returns with a striking shred of evidence, but for some reason, they are not prosecuted further. Perhaps NY doesn't consider animal kidnapping punishable enough, but it should be.
George's Role In Susan's Death
Granted, this was completely accidental, and a direct result of George's "cheapness", but the fact remains that he is the one who point-blank demands that his fiancee settle for the low-quality envelopes.
In fact, the shopkeeper even makes it a point of mentioning that the glue on the envelopes he wants to buy isn't adhesive and requires "a lot of moisture to make them stick", as well as claims that they haven't been produced in a long time. A good prosecutor would have certainly been able to make the case stick with this much information, and George potentially might have gone to prison.
Jerry Drugging His Date
This one is point-blank criminal — Jerry, whose new girlfriend has a rare collection of toys, desperately desires to play with them, but she refuses his pleas, stating that they aren't meant to be opened as they would lose their value.
To ensure the fruition of his plan, he callously spikes her drink with drugs, so he can have his fun while she lies unconscious on her couch. The moral turpitude of this scheme offends even Kramer, which is saying something.
Kramer Accidentally Injuring His Girlfriend
George's parking spot mishap turns ugly, but it gets worse when Kramer wants to purchase a new wheelchair for Lola whose older one is damaged. Unfortunately, both of them opt for a used model in order to save money, without considering the dangers it might pose to the user.
As expected, Lola rolls straight down a sharp incline because, as it turns out, the brakes on her device turn out to be non-functional. She appears to testify against the gang in the final episode as well, but she could have easily done so on the spot and successfully accused Kramer and George of injuring her intentionally.
Jerry and Kramer Involved In Cockfighting
Cockfighting is an illegal sport, mostly because it is horrifically inhumane, so the fact that Kramer and Jerry decide to take part in it, by putting their new "pet", Little Jerry, in the ring, is grounds enough for a solid case against them.
Although Kramer is poetically punished by Little Jerry's opponent's beak and claws, this doesn't mean that the two of them are safe from the legal repercussions of their actions. The only question is who would have ratted them out to the cops.
George's Attempt At "Murder"
After the whole Cuban Cigar manufacturing fiasco, Kramer gets the Dominican immigrants a job "rolling crepes", but they inadvertently do so with such force that they burst open and scorch innocent diners. One of them is Neil, a man that George is obsessed with, and due to this event, Danielle decides to stay with the former, instead.
Enraged by these developments, George decides to take revenge on the injured man by sneakily plucking out his IV line. To be fair, Neil isn't so badly hurt that this act would have killed him, but who knows how a skilled lawyer would spin it in court?
Kramer's Failed Kramerica Enterprises
Kramer may come up with some ingenious ideas, but his Kramerica company ends up in trouble after their rubber-bladder test goes horribly wrong. He and his intern from NYU, Darin, toss a gigantic rubber ball from a high floor in George's new company, which promptly injures Claire, Jerry's new love interest.
She sues Play Now, which results in George's job loss, and Darin going to jail after accepting his guilt in the matter. Kramer slips away to freedom, even though the whole idea had been his brainchild from the start.
Jerry Becoming A Bootlegger's Bootlegger
Jerry takes Kramer and his pal, Brody, to watch Death Blow at a special screening, where he is aghast to learn that the latter is a bootlegger. He is subsequently threatened to complete the task when Brody inexplicably becomes ill, but soon grows to love his supposed "genius" at the job when Brody is impressed by his work.
Unfortunately, Jerry's ego swells a bit too far, and insists that they bootleg another flick, Cry, Cry Again with multiple cameras and recording devices. This is rejected by Brody, which is the only thing that saves Jerry from getting embroiled in yet another crime.
George's Charity Scam
George Costanza, in yet another bid to save money, tries to avoid the whole Christmas gift rigmarole by inventing the fictional charity known as The Human Fund. He goes so far as to collect a massive amount of money from his colleagues, but Mr. Kruger, his boss, is upset to discover that there never has been such a thing.
Instead of being furious at George for siphoning company money, his boss is more annoyed that he receives a "fake Christmas gift". In reality, this falls under embezzlement and misappropriation, which should have landed him several years in prison.