I would first caution you not to assume people are very angry unless they tell you they are. What some people see as angry, negative, bitter etc are other people’s normal forms of expression based on their personality and culture. I have been called all of those things by people who wanted to see me that way, or people who were not used to a female who didn’t act "girly ". I actually wasn’t any of those things.
Second, assuming your judgment is right and the person is angry, give them the benefit of the doubt that they just need to blow off some steam. I know several people who are actually pretty happy with good lives but they can blow a gasket over something fairly minor they read in the newspaper or hear a boss say at work. They flare up, holler for a while and have usually set it aside within a few hours or a day. Often they grew up in a culture where emotions were expressed this way, by getting excited. They aren’t really that angry.
Third, let’s assume the person is really chronically angry. They may well have a legit reason to be angry and be working through it. We all have times in our life when somebody or something really makes us mad or disappoints us in a big way and we can’t just get over it like that. Pray for the person. If possible, let them talk to you about their anger (say something like “you seem really angry, what’s really making you mad? Tell me” and listen to them when they talk). Give them time to get past their anger. If and when they are ready, they will. Above all, don’t tell them anger is bad or unhealthy etc and to just “let it go”. I personally think anger is just something to be worked through and demonizing it just pushes it further inside, and THEN it’s unhealthy because it’s being suppressed and will just manifest in some other way like illness or acting out.
