Some people you can either shoot or ignore, but there isn't much else to do with them.
When someone has displaced anger because they have serious life issues that they can't or won't face, and won't even admit, you have one of two choices.
One, you can tell them what their real problem is, in terms they can not misunderstand. You might as well shoot them, given that there are reasons for denial that have nothing to do with Egypt ("De Nile, it isn't just a river" is an old saying in some parts of the country). The sister who is upset with her life choices and her husband, but who won't admit it and who can't do anything about it, so she gets angry with everyone else is a good example.
Two, you can treat the outbursts and the venting like you would Tourette's Syndrome. or some else's three month old baby who is crying because of a full diaper.
There is no point in taking them seriously, or taking what they say to heart if they vent in your direction. As long as they can't do you harm, the right response is to feel compassion and let them vent like you would someone passing gas by accident. Don't dwell on it.
And don't worry about disabusing them either. Try it two or three times and then recognize what is going on for what it is -- displaced self-anger. In my own experience, having thought someone just had mistaken anger and having worked them through their resentments several times until they decided they didn't want to talk with me again (they needed their resentments and coming up with new ones was hard), all you can do is be kind.
Or, you can shoot them. Point out that they are wrong on whatever they are venting about, then tell them bluntly the real source of their anger and challenge them to deal with it. Do it in a way that informs those around them of the issue as well.
I can give examples. People in grief sometimes act this way, but most of them grow out of it, and those that don't usually are grateful to find help in recognizing the displacement so that they can find recovery. The tools are useful, the problem is that people who have problems from other sources (e.g. the hyper-competitive mother whose kids aren't that smart, good-looking or athletic, or the guy who is too ugly but wants pretty girls not to judge him on the same criteria he judges them, or the person who is married to a spouse who isn't bad enough to divorce, but who isn't as special as they thought, or ...) are not ready to respond to them.
Until they are ready to come into the light and quit lying to themselves, there isn't much you can do. I wish there was. Not every tool should be used in every situation.