Being critical versus critical thinking
Paralleling the difference between arguing and reasoned argument, there is a difference between being critical and critical thinking. Just as the careful structure of an argument is an essential part of quality argumentation, critical thinking implies that one is paying careful attention to whatever is studied.
Being critical is synonymous with ranting, complaining, or, at times, undermining someone else's efforts. Being critical for the sake of being critical is often fuelled by emotion, especially anger. In contrast, being an effective critical thinker means that you can analyze your object of study in a fair and reasoned manner; moreover, the analysis has a purpose, and often a helpful one. After evaluating what you have analyzed, according to a fair standard of evaluation, you may deliver some constructive criticism.
To summarize, while being critical involves being emotionally upset, unfairly picking on someone or something, and not offering constructive solutions (as well as possible means to implement them), critical thinking is an analytical skill built around the principle of charity and the principle of cooperation.