Among the groups of people whom Halacha disqualifies from serving as witnesses is that of "Bezuyim," meaning, people who act in a self-degrading, shameless manner. Such people are disqualified from serving as witnesses "Mi’de’rabbanan" (by force of Rabbinic enactment).
An example of this kind of character is somebody who regularly eats full meals while walking through the street. Eating meals – such as a sandwich, or pizza – while walking through the street is considered undignified, and reflects a lack of self-respect. Therefore, somebody who conducts himself in this manner on a regular basis may not serve as a witness. This also applies to people who do not wear proper clothing outdoors, while they work or conduct their personal affairs. Such people who show no concern for their personal dignity are looked upon not as people, but as animals. As such, we cannot trust them to speak truthfully in court, and they are therefore disqualified from serving as witnesses.
This reminds us of the importance of selecting as witnesses (such as at weddings and the like) people who maintain high standards of ethical and refined conduct. Even those who do not commit specific Torah violations are unsuitable for this role if they regularly act in an unbecoming and undignified manner.
