Five tips to handle a hothead
It is always tricky working with someone who is quickly angered and walking on eggshells just so you don't set them off is not a solution.
If you value your life and sanity, then by no means should you ever utter these two seemingly harmless words. Telling a hothead to calm down is as good as asking a fish to ride a bicycle. In fact, you will probably set them off further. Don't expect logic to work here either because they are not in the most practical frame of mind. The best thing to do is to wait for a few moments and let them rant.
Address the issue
However, do not let the rant run on indefinitely because the more they get into it, the more they think they are justified in their anger. After a minute or so, address the issue with them. Pinpoint what is making them angry and say something along the lines of, "I understand you're angry because I missed the deadline/ate your sandwich." This lets the matchstick man know that you get why he's losing his cool and it allows you to move forward to a solution.
Ask them what they need or how you can help. This forces them to stop fuming and be constructive about the issue. The angry person feels that the situation is unfair towards them, so offering a solution can make them open their eyes and see that the problem is not as irreparable as they are making it out to be. Using phrases such as, "I will set a new deadline/replace your sandwich," will help steer the rant into a proactive space.
It's easy to not feel heard when you're dealing with a hothead, but fighting fire with fire isn't going to work. To settle the situation quickly, you need to keep your cool no matter how agitated you are getting as well. Talk in a mild tone. Counting in your head and being logical will also prevent the situation from escalating.
Use your words
When talking to a hothead, make it clear to him that you are finding fault with the communication, not the person or the situation. Statements such as, "I don't think we are communicating effectively," or "Let's take a breather and get back to this," work much better than, "You're too angry to think clearly," or "Why are you making such a big deal?" If the hothead feels that he or she is being understood and not attacked, they are likely to cool down quicker.