Keep calm and carry on. Truly, don’t react with emotions such as frustration or anger. Rather, take rejection in stride and move on to the next meal.
Don’t give up on a particular food after rejection because most children need to see, smell, touch, and experience an unfamiliar food several times before they are brave enough to try it, or even like it. This is particularly true with vegetables, which tend to have a bitter taste. So, bring that food back to the meal table in a few days, and try again!