Anger is a common reaction that is the result of failure, fear and sensation of pain. Anger is a sign of wound, damage and sensitivity. The one who suffers from anger issues is actually needing help even if it doesn't seem so.
Everyone has a threshold for emotions, after which their tolerance towards their situations fade.
There will be people around you who walk angrily, waiting to burst at any moment and take it all out. You'll notice that they get irritated with small issues and show unexplained anger towards things that don't even make one angry.
Before judging and backfiring at them, take into consideration the reasons as to what made him/her angry so fast. Just when you think - "But this isn't even something to get angry on" or "why take it out on me? What did I do" is exactly when you should calm down and look for the hidden reasons.
There are numerous reasons for anger like childhood trauma, improper upbringing, likewise parents, personal conflicts, emotional unhealed wounds, lack of love etc.
These outbursts of unexplained anger can be due to their emotions that went unnoticed or were ignored earlier, leading to its its suppression and a buildup over a period of time.
We all have our own struggles. An inability to handle them and expectations of quick results, often leads to frustration and anxiety. Under such circumstances, the threshold of tolerance goes down, the suppressed emotions surface in the form of anger.
What looks like unnecessary/unexplained anger to you, might actually have 100's of reasons. So instead of taking it personally, be patient enough to look through the anger. This will help you get a solution by being more compassionate and understanding towards each other. - Pritesh