Anger is like a practiced skill. So is dealing with it. Speaking from personal experience, its best not to 'just ignore it', but give it a clear time and space for handling it, looking into whatever is causing it then leaving it there. Even if you can't control the causes of it, ritual action can help you manage the personal impact of it. Sitting down, meditating on the issue (just thinking through what is going on, how it has happened, and examining it through the lens of emotion, then following the threads of emotions until you understand the connections and what is causing it to linger) followed by token action to deal with the causes is enough that you can tech your friend/acquaintance to better deal with his anger issues.  Overall when you are in front of an angry person, being calm it s your best choice, as it deflate the tension. Later on you can follow up and try to reason with the same person, when he's/she's in a better state thus more receptive.