How do you make someone less likely to get angry?

Be very careful of what you say; think before you speak; whatever you say to them, would you like it if those Words were spoken to you?

For example, you feel like yelling, "You're not helping!" at a friend trying to help you do something. If you're trying very hard to help your friend do something, you wouldn't want your friend to suddenly utter, "You're not helping!"