Some wisdom inspired by my fighting parents
 
As soon as someone begins a sentence with "You should" or "You need to" my guard goes up and I start to formulate my "lines of defense." Even worse than a "you should" start, is when my interlocutor commences with "You should have." The appropraite reply to unsolicited advice depends upon your relationship with the opinionated person and whether or not you care about continuing that relationship. Here are some suggestions to help you tell your opinionated coworker, friend, or relative: “Stop should-ing on me.”
 
If my boss tells me that I need to do something or improve something, a "yes, boss," is often the best answer, or possibly, "I'm right on top of that Rose," to quote a forgotten nineties movie. If a task is requested outside of your normal range of tasks, or if you are not aware of its priority status, follow up with a clarification question. 
 
Dealing with annoying coworkers (thankfully I do not have of those) is an entirely different ball game. If your cubicle comrade has been trying to tell you how to live your life for a long time, you may want to tell them to take their unsolicited advice and shove it, or ask them why they think they are God. However, do keep in mind that such replies are generally not well received. Sometimes a simple reply of, "I'll take that into consideration, “or "Hmm. I hadn't thought of that," is enough to keep the peace. Ultimately, if the "you shoulds" and "you need to's" never stop and involve non work related matters, you may want to just nod and have pocket replies to cut the conversation short. "I would love to talk, but I am swamped right now," can do the trick, or for even more long term benefit you can try: "I wish I was able to multitask better so I could listen to you and work at the same time, but unfortunately I really need to focus on getting this done right now. I will definitely mull over your opinion."
 
For the most part, no one really likes to hear unsolicited suggestions about how to do their job, raise their children, style their hair, or live their life. Perhaps it reminds us of our parents or insinuates that we are incapable of making our own decisions. As a general rule, unless you are in a position of responsibility and giving a command or advice to a subordinate, keep your opinions to yourself.
 

If you find that you are raging due to the constant barrage of "feedback" or "suggestions" from someone with no authority to give them, then I suggest taking the conversation outside. When I say "outside" I am not referring to the office equivalent of a bar fight equivalent, but rather to a leisurely stroll somewhere with a tree or two. I have found that when in nature or engaging in physical activity it is much easier to let your defenses down and have a more open and honest conversation about communication and conflict.
 
You should print this post for future reference...:) Now what have you to say to that?