We may have known or met someone many times but may not know their true personality because when we meet people during happy times, they present their best behaviour.
Undoubtedly, stress can lead to anger and frustration, and a person may deviate from their normal behaviour, but such deviation is often minor and temporary. Some people become so agitated that they become harsh, impolite and disrespectful.
No matter the situation, one needs to learn to deal with their problems rather than blaming or putting others down. The stressful time won't last, but the damage to the relationship because of your behaviour could be long-term.