Rudeness is generally defined as a display of disrespect, a breaking of social norms or expectations, a breach of etiquette, or ignoring "accepted" behavior. It can also mean someone behaving inconsiderately, aggressively or deliberately offensively.
The word "accepted" is important, because rudeness can mean different things to different people, or within different organizations or environments. For example, shouting and swearing might be considered normal in a busy restaurant kitchen or on a construction site, but it would be regarded as inappropriate and unacceptable in most offices.
Similarly, there can be cultural differences to consider. For example, in Japan, something as seemingly innocent as laughing with your mouth open is a no-no. So, it's important to be aware of possible cultural faux pas, especially if you are working with a culturally diverse team.
Rudeness can be a way of displaying power, trying to get your own way, or provoking a reaction. It can also be a response to stress, pressure, frustration, or some other form of unhappiness and may lead to aggressive and bullying behavior.
According to a study in the Academy of Management Journal, rudeness can seriously damage team morale and performance, reduce helpfulness and collaboration, and negatively impact workplace productivity and relationships.