No! People lie all the time, lying is simply part of social interaction.
Try being honest to everybody: "you stink, your kids are ugly, what's wrong with your hair, I want to have sex with your girlfriend, etc. etc." ... Many people don't appreciate honesty, because honesty is often just plain rude.
So we lie. Kids learn it at a young age, the trick is to teach them when it is okay and when it isn't okay.
Um... if someone stinks then tell him or not. No lie needed. I would kick anyone out who lies clearly to me on such matter. So in practice say it if you are near him or don't mention it. No lie needed. With ugly kids... why say something at all? He can't change anything with it. And if he asks then say something diplomatic... like "That child has nice hair" or whatever. If you can't find anything say that you don't want to answer, do as you did not hear the question and speak about something different or say something like that there are prettier ones at worst. No need to lie. In fact I would assume a parent would know the truth and such question would be a test about your character. Brownnose or honest person.
Your girlfriend should be happy if you ask her what she did with your hair and there are so many ways to say something that you won't offend.
I wonder why this black white view is seen by some on that topic.