Truth- really?

While I was working at Pete's the other day I came across a question from a customer at the bar that sparked me to keep bringing up the importance of truth. The question of when is it okay to lie came up while I was looking for a beer that we were out of. A fellow bartender told me to give the customer a beer which was extremely close to it- I told him no because that is dishonest and the customer will most likely be able to tell. A customer at the bar piped in and said that no, it is okay to lie to this customer. And against my best judgement I served the beer, telling the bartender and the customer lying will come to bite them in the end. Fast-foward to the moral of the story, the customer came up to the bar and said it didn't taste like what she ordered. I gave the two guys the I told you so look. After that is when it sparked the question about lying. The customer said that it's okay to lie to a significant other if needed, I disagree with him and stood by it. I believe that it is essential to tell the truth, even if the truth hurts.
As I was watching Randy Pausch's Last Lecture online the other night, he explained his philosophy about telling the truth. He brought this into the classes he taught, to have the students critique each other, honestly. But importantly it is about characteristics through group projects. I will definitely bring that into the classes I teach, I think that element is crucial to teach. I remember disliking group projects because of the usual reasons- I am hoping (it might not happen) but if putting the characteristics to critique as well, it might change some mindsets of teenagers. But again, I might be putting too much faith into them for this to occur, thus, the reason why I want to eventually go for that PhD so I can teach college students who are in college for a reason; that will work for it.