Start with something supportive. Point out where you agree with him/ her. Do not fake it, but you can always find something positive about another person, particularly if you are not judging.
State your opinion using “I” statements. “I” statements are always carefully phrased so that you are acknowledging your point of view with no hint of negativity toward the opinion of the recipient. An example of an “I” statement is, “When you interrupt (specific behavior), I feel you do not value my input to the group (expression of your thoughts or feelings), and I would like for you to not interrupt me when I am talking (behavior-change request).” A person is less defensive when you use a specific example and identify your thoughts and feelings (versus saying, “You made me…”). Remember that you are making a behavior-change request of the person—you cannot make the other person change her/his behavior.
Monitor your tone of voice and body language. Sarcasm can be conveyed totally by tone of voice, and we are often unaware of our tone of voice unless we pay attention to it. Also, monitor body language and increase your awareness of the messages that your body language might convey.
You can tell if you are following these suggestions effectively by watching the observer. If they get (or continue to be) hot under the collar, you have not succeeded. Understand, of course, that sometimes the recipient may be angry, no matter what you do, but, if you try these techniques, odds are the other person will listen to you. For many people, giving and receiving constructive criticism is difficult. Asking a teammate to facilitate may help.