Manners and etiquette, social lubricant or acceptable dishonesty?

This coming Wednesday,  we are discussing the acceptable dishonesty in the name of good manners at the Ideas Cafe.

We all know that liars cannot be trusted as we don't know when they are not telling the truth and therefore have to assume that they may not be telling the truth and therefore do not depend on what they say.

However, when someone is not telling the truth because of "politeness",  we all make exceptions and trust that this "polite" person will be honest in other situations (except when it involve manners).

No doubt,  this is to make allowances for our sensibilities of being easily offended by criticisms and negative opinions of our appearance, behavior, or thoughts.

Politeness lubricate the awkward initial social situation setting participants up in a positive mood to react favourably with the group they are socialising with.

It continues until participants feel comfortable enough to be more truthful as they get to know the others better.

Nevertheless, there are some strict exceptions:

Take the standard example of a guest's reaction to a mediocre dinner by the host or hostess.

Is it inconsiderate for a guest to not gush over a hostess' less than perfect dinner, but should the guest not also offer helpful advice on how to improve on the meal for next time?  

That will likely be received as a criticism even if it will improve the quality of future meals.

Do we need to develop a thicker skin as host and hostess so that we are not offended so easily and can benefit more from the helpful input?

Or perhaps we need to lower our expectation of what our competence level is so that we expect helpful suggestions without seeing it in the light of a criticism?

As guests, should we not try to help the host improve instead of fooling him one more time that he is the perfect chef and set him up for the next less than perfect meal?

How do we ourselves recognize our emotional reaction to criticism and contrary opinion?  How do we separate helpful suggestion from truly hurtful remarks?

If we all know that good manners require guests to be complimentary, why do we still feel good about being paid these compliments?

Who determines etiquette?  Is it similar to fashion with leaders and followers?  Can we start our own etiquette code?

Are we better to trust opinions of strangers and anonymous feedback over comments from our friends and family as the latter tend to be more considerate and less truthful?

Are true friends and close family suppose to be brutally honest or warmly supportive?

Let's have your brutally honest ideas this Wednesday!