Which of the Ten Commandments is most misunderstood?

Many (if not all) of the Ten Commandments are misunderstood.

For years, the English translation "Thou shalt not kill" prevented many Christians from fighting as soldiers in wars. The correct Jewish translation is "Thou shalt not murder" which allow for the killing of enemy combatants during a "just" war. Considering that God commanded Joshua and the Hebrew to kill all the people of Jericho would itself break the law if killing was not allowed.

In the Sermon on the Mount in book of Matthew chapter 5, people were reminded that committing adultery was committed even if one looks lustfully at a women.

Likewise, there is much confusion of observation of the Sabbath for Christians.