A lie must have intent otherwise is it an error. In your examples, saying yes to the boss's gift is definitely a lie. It is a lie based on a motivation to be polite, but still a lie and intentional deception all the same.

"World's best Pizza" is definitely a lie, and yes, it is intended to deceive the reader into having a falsely grand idea of the quality of the product. Because this type of language is so over-used as to be ineffective, does not absolve it of the motivation to deceive.

"I went to the moon," is definitely a lie and clearly deception because you are avoiding telling the truth. Even a technically true statement, when used to deceive or distract, is still a lie. For example, you catch a child making a mess, you ask, "did you do it?" and they reply, "Mommmy I love you." The statement ouf of context may be true but in this situation it is clearly used as a lie to distract the listener from the mess.

In almost all instances that I have seen, this phrase follows a comment which could be critical, controversial, incendiary, or rude. Tacking it on the end of a sentence usually implies, "but don't get defensive," or "I don't want an argument." However, because it withdraws the critic from the critical statement issued, this makes it all the more frustrating to reply to.