Contempt vs Regret: They look similar in terms of facial expression. To know the difference, start with looking for the movement of the head. When showing contempt for another person, there will typically be a distancing gesture or raising of the chin giving an arrogance display.
With regret, there will be a downward casting of the eyes or moving of the head to the side. There may even be a shaking of the head in a “no” gesture. Keep in mind, regret and contempt are virtually the same emotion (negative opinion of something, someone or event). What differs is the target and secondary emotion: Contempt is more commonly reserved for others, regret is for yourself or something related to you. For example, if the losing QB of the Super Bowl played a great game but lost, you should see regret for his team’s performance (if you see contempt, he is blaming his teammates and putting them below him- not good).
As stated earlier, contempt and regret are both negative emotions. When considering the blending of the emotions, we must understand that contempt is a negative opinion blended with anger (or one of its variants such as frustration, annoyance, etc.) or disgust. Regret is a negative opinion blended with sadness.
The anger/disgust in contempt will give the display the distinctive jaw thrust and distancing posture. The sadness in regret will give the emotional display its partial frown and downward gaze.