Something that is egregious stands out, but not in a good way — it means "really bad or offensive." If you make an egregious error during a championship soccer match, your coach might bench you for the rest of the game.
An egregious error is so bad that it might not be forgivable. Some synonyms are appalling and intolerable. The word has made a 180-degree turn from its original sense in Latin, when it meant "exceptionally good." Word historians have speculated that the negative usage was originally meant to be ironic, but it is the only sense that has survived. Be careful not to use it to mean "outstanding," since no one wants to be called egregious.