Feedback and critique
Feedback can come in various forms, including advice, compliments, ambiguous remarks, big picture insights, etc. Learn how to listen carefully and diligently to what is being said so you can translate the feedback to be understandable, useful, and ultimately actionable. If someone gives you ambiguous feedback, this means that they can intuitively see a weakness but might not know why something isn't working. You should follow up with their comments with probing questions to better understand their perspective.
If an instructor gives you advice and that they want you to do something, you should try it and see if it works. If it doesn't work well, then bring that up in the next critique. The instructor is not responsible for the choices you make when creating work, only for guiding and responding to those choices. If you make work that is sub-par as a result of the instructor asking you to try something, don't blame the instructor. You should have the ability to identify emergent weaknesses that the instructor did not anticipate, and pivot before showing that work in the next critique.
Interpreting feedback
Let's say you just pulled an all-nighter to get a project finished (unfortunately very common for art and design students). It's a masterpiece, and you can't wait to unveil it to unfettered acclaim from your peers. However, you show your work to everyone, and the response you get does not sound like praise. In fact, they say things like "it's not working" or "I don't understand why you did that ..." and you are devastated.
Unless you had brutally honest parents growing up, you might not be used to a negative response to your creative work, particularly work in which you have invested considerable effort. Letting go of emotional attachment to your work will greatly help you with the ability to self-evaluate more objectively. That "eye" that people mention that perhaps got you into the field in the first place comes from this ability to objectively evaluate. Praise can certainly happen in feedback or critique and is a great way to communicate when you've done something well, but you should remain skeptical of too much praise. Unwarranted praise can really hold your work back, blinding you from where your weaknesses lie. If your work needs improvement, you need to know about it in order to improve, and this is the main goal of feedback.
Though feedback typically centers on your work, sometimes comments are aimed at you and not your work. The emotional trauma of being criticized can be painful. Step back and remind yourself that the purpose of the feedback is to help and encourage you, not to be condescending or cruel. This objectivity is really important so that you can learn from the feedback. Some students have trouble trying anything outside of their comfort zone. This is often obvious in a feedback session or critique. Signs include defensiveness to negative feedback, sense of arrogance or overconfidence, dismissal of instructor comments or suggestions, and outright refusal to make changes according to feedback. This is not a professional attitude or outlook, and will keep you from the opportunities that will grow you as an artist or designer. Failure must happen rapidly so you can improve at a quick pace. Closed-mindedness causes failure to happen slowly over a long period of time. Your instructors are genuinely invested in your success and it is their job to point out shortcomings. Most student interpretations of overt "insensitivity" or "hardness" by an instructor typically results from a situation such as the one described.
Giving feedback
Keep it positive. A tried and true technique for feedback, where appropriate, is called the "critique sandwich." This is the Happy Meal of the critique process. Essentially, you will start and end a critique with positive comments (the bread), using the comments in between (the meat or meat-flavored tofu) for the important, possibly negative-sounding feedback. This makes hard-to-swallow comments more palatable, yet still communicates the important issues.
Trolling
Anyone can intentionally or unintentionally become a troll. A troll is a person who is intent on disrupting constructive discussion by posting inflammatory remarks to halt the progress of a discussion — typically for the purpose of self-amusement or for the emotional high of winning an argument. This happens in online (and sometimes offline) spaces that lack established social norms or policy enforcement.
In an academic setting, the instructor sets the social norms of the classroom and maintains authority over moderating a discussion. It is not an instructor's job to be "thought police." Therefore, if a student has an opinion that is counter to the general opinions of the class, voicing those opinions are encouraged to provoke thoughtful discussion. However, disrespectful remarks meant to oppress another student will be considered trolling behavior and will not be allowed to continue without consequence.
Trolling is the antithetical to meaningful discussion and learning, so try to be mindful that your remarks (possibly being written under some emotional stress) don't accidentally veer off course and shut down a potentially helpful conversation.