Nobody likes it when people are rude to them, but we don’t like it when people are rude to other people, either. Have you ever flinched when a customer was rude to a cashier? That’s what we’re talking about. According to MSNBC, rude behavior makes us feel uncomfortable and conflicted, and witnessing rudeness can spoil a meal, ruin a good mood, kill creativity, hurt job performance, and even put people’s lives at risk in the hospital. Customers who witness one worker berating another are often so distressed that they’ll never come back, ever.

So, why does rudeness directed at others make us so uncomfortable? Dr. Christine Porath from Georgetown University, who studied rudeness, says that we see it as an act of aggression that could escalate out of control. It also offends our sense of justice, and leaves us torn. Most of us want to avoid conflict, but we’re also wired with mirror neurons – which make us feel empathy, and we feel anxiety if we don’t do anything to stop it.

In one study, researchers at the University of Aberdeen in Scotland looked at how common rudeness is in healthcare. According to their survey of several hospitals, two-thirds of operating room staff had been treated rudely and aggressively by nurses and doctors. Or had witnessed arguments between operating room staff. The impact of the rudeness: distraction and reduced job performance. Not something any patient wants in a medical environment.

Rudeness can also affect a company’s bottom line. In another workplace study, volunteers watched one of three videos set in a national bookstore chain. One showed an incompetent cashier. Another showed the manager screaming at the cashier for chatting on the phone with a friend while customers waited.  In the third, the manager politely asked the cashier to hang up and take the next customer. The result: The people who watched the rude interaction got angry at the store, and vowed they’d never go there to shop.