Recognizing invalidating statements, words that tell your child that he doesn't think or feel in the right way and he must never listen to himself because of this failing, often fall into the following categories:
Trying to get the child to question himself. What were you thinking is an example. In other words, you're an idiot. Hardly builds the child's confidence in his decision making skills.
Ordering the child to feel differently. Stop crying. Smile. How can you be friends with... In other words, don't feel the way you feel.
Debating: That's not true. How can you say that.
Inducing guilt: I tried to help you. You are making everyone else miserable.
Judging and Labeling: You're such a baby. You are too sensitive.
Telling the child how he should feel: You should be thrilled. You should be grateful.
Defending the other person: I'm sure you must have done something for him to react that way. Maybe she was just having a bad day.
The first step is awareness. Even and perhaps especially well-intentioned parents can be invalidating, because they don't want their childrent to be unhappy. Facing suffering is a skill that must be learned. You can't protect your child from suffering in life, so consider how to prepare them to best handle it.