In tractate megila of the Babylonian talmud the sages say that it is forbidden to look into the face of a wicked person. What is the reason for this prohibition?
Rav Avigdor Miller was asked this same question:
Q: What is the problem with looking at the face of a wicked person? [אסור לאדם להסתכל בצלם דמות אדם רשע – “It is forbidden for one to gaze at the face (image) of a wicked person” (Megillah 28a). ]
A: If you look at the face of a רשע, you become a רשע. And I’ll tell you why. We are influenced by people. And the face of רשע is a screen. It’s a projector. And his נשמה projects its image on that screen. So his רשעות is on his face. You might not recognize it, you might not see it, but the רשעות is on his face. And when you look at his face, it becomes stamped on your נשמה. What you see is stamped on your נשמה.
1) That’s very important. What you see will affect you. Don’t be מסתכל בפני רשע. Don’t look at the face of wicked people. And don’t look at people doing wrong things. As much as possible, avoid getting the stamp of wrong things on your נשמה.
2) And I want to tell you something else – another reason. Hashem doesn’t like the רשעים. A רשע is busy frustrating his own purpose in life and is busy ruining others as well. And Hashem is disgusted with that. Now, when someone feels disgust with somebody else, if you’re really disgusted by someone, then you don’t even want to look at that person. And Hashem doesn’t want to look at the רשעים. And if you walk in the ways of Hashem, you will also be disgusted by the רשע and his behavior. You don’t even want to see him. You don’t want to look at his face. And that’s why we don’t look at the face of a רשע. We are training ourselves to be disgusted with those who disgust Hashem.