It seems like the character of Tantalus changes pretty drastically depending on which version of his story you read. Depending on which kind of crime he commits, he definitely becomes a different kind of dude. In one version, he hides a golden dog for a guy named Pandereus, who stole it from a temple of Zeus. When Hermes shows up to question him about it, Tantalus totally lies about the whole thing. Okay, so this makes Tantalus a liar and a participant in the apparently thriving golden dog black market, but it's definitely not the worst crime that Tantalus is accused of by other writers.
We're going to go out on a limb and say that most people would think that Tantalus's whole foray into fine dining is his worst possible crime. In some versions, Tantalus chops up his son Pelops, boils him in a pot, and tries to serve to the gods at a dinner party. (Every time we write that it seems like it's more messed up.) Tantalus says he does this to test just how all-knowing the gods really are. Are we crazy, or are there a lot other ways one can test the gods, which don't include dismembering and cooking your son? In this telling of the tale, Tantalus seems to come off as sadistic and downright deranged.
In other versions of the story, Tantalus is punished for sharing the divine secrets, told to him by his father Zeus, with other mortals. Tantalus is far from the only mythological figure punished for this sort of thing. Probably the most famous is Prometheus, who was punished horribly by Zeus for giving man the secret of fire. Interestingly, Prometheus tends to be viewed as a hero for giving man valuable knowledge, despite the fact that he defied the gods. Tantalus, on the other hand, is almost always thought of as one bad mamma jamma. Could it be that the darker versions of the story have totally tainted the T-man's reputation?