My child will turn 3 in April and hasn't said this exactly yet to me but she will have an emotional outburst out of anger and will shout, "I'm angry!" or "I'm frustrated" when she is frustrated. This is a result of us defining our emotions when the parents feel it themselves. When I feel frustrated, I say aloud, "I'm feeling frustrated" to get me to calm down and to define the feeling for her so she knows what it can look like and what might provoke a person to feel that way. We also define positive emotions (proud, happy, excited).
We have always taken the approach of talking about our feelings so I ask her why she feels angry to learn her reason or a recap to dig further. I do not disagree and say, "that shouldn't make you angry" or "I don't think I'm mean." I think that is invalidating their feelings.
My daughter watched Disney's Brave and the daughter says to the mom, "You're a beast!" so she was saying that to me for a bit. I knew it was in jest and knew where it came from. But I would still respond with, "Oh yes Merida said that to her mom because she was angry with her. It really hurt the Queen to hear that. Merida should have talked to her mom about it instead of running away." She stopped saying it when she forgot about it and we haven't seen the movie for a long time now to remind her.
We also have a zero tolerance for tantrums. We do not entertain any requests if she is throwing a tantrum. We ask her to calm down and to ask again. When she is calm we listen. There is of course the difference of noticing when a child feels slighted and a tantrum from being spoiled from something. Absolutely consistency is key. Many times they do something repetitively to see if they get the same response (just like dropping things from the high chair) :)
EDIT: Also, I had read something before about not bothering to reason with children under 7 but I always gave a reason. Since she was a baby I would say that the #1 rule was she was safe and #2 was she was having fun. So when she cried (and was not yet expressing her emotion at that point to add feeling to the crying), I would just ask, "what's number one?" and she would say "Sydney's safe." So she knew it was out of love and not me trying to spoil her fun. This has worked very well for us to shorten crying bouts. And I followed with a reason as well, "it's dangerous" or "when your legs get longer, that will be something to try". Now she is becoming a stiff negotiator.