Criticism is great, but it should be done appropriately. Instead of telling someone how much X sucks, tell them that, in your opinion, X they might be able to make X much better by doing A, B, and C. This is difficult to do appropriately, but very helpful to everyone.

It is also difficult and important to learn to listen to criticism. However, you can probably screw up your life much quicker by giving criticism in an undiplomatic way than by failing to take criticism.