Does my bum look big?
Who is being a better friend: someone who tells the painful truth, or someone who tells little white lies to save you from embarassment?
We're not sure, either.
The difference between constructive criticism and saving someone's feelings is that being constructive shows the other person that you are interested in what they are doing. And that you want to help them get around the problem.
It works both ways; generally try to take criticism constructively too. If someone is giving you their opinion and advice, take the personal out of it, listen and respond to the useful stuff.
Giving constructive criticism
1. Aim to give two positive comments for each negative one.
2. Try to base what you say on a suggestion "another option could be…", "have you thought about…" rather than an instruction.
3. Avoid statements that don't explain why you're saying them: "I don't like it.", "It was fine as it was", "You should do it again."
4. Only include a few points of criticism and stay with the most important ones. Criticism shouldn't be vague, always let the person understand exactly what you mean.