Lies... When are they acceptable?

So I haven't been on the computer in a very long time because I've been so busy. But I've been, shall we say, inspired by some recent events.
My little sister has been annoying me alot lately. And my biggest problem with her is that she lies and won't own up to things. But I've also noticed that she has lied to some of her friends sometimes to keep her out of trouble. While I think her lies are ridiculous and I CANNOT stand them, I also thim some of her lies are valid.
I, obviosly, have lied before myself, so who am I to judge? Once again, I'm trying to leave my judgement to Jesus, but it is a very hard concept (even for one who preaches it, lol).
I have lied to my parents about things that I was afraid of getting in trouble for, and I felt very bad about it because nobody should lie to those who care about you. But there have been times that I've needed to lie to protect myself from people who might hurt me or help me get myself into trouble. Those people I like to call catalysts. They speed up the reaction, basically, to help you get into trouble.
Well, last year a friend asked me to smoke weed. I just about flipped out (in my mind), because I had NO IDEA she was doing that, and would have never thought she would have tried to get me to do that. So I kept my cool and told her that my asthma was bothering me the past couple of days. Well, obviously, that was NOT the appropriate answer. But it protected me for a time, so that I could collect myself and tell her the truth and also tell her how IDIOTIC it was for her to be doing drugs of ANY sort.
The lie bought me time to escape from her, the catalyst.
An example of this in the Bible is the snake asking Eve whether or not the Lord said not to eat the forbidden fruit. Eve said that the Lord did say not to eat it. Then for her protection she also said that God told her not to touch it either. A lie. God had never said that she couldn't touch the fruit, just not to eat it or else she would die.
This lie was an attempt at self-preservation, protection, whether it worked or not. I think it was quite smart of Eve to set that extra rule even if the snake was still cunning enough to convince her to eat it anyways.

Abraham lied and said that his wife, Sarah, was really his sister so that he would not be killed because she was so beautiful and another man would want to take her for his own.

Well those are two examples. I need to get some sleep. God DOES NOT condone lies, but if you have to lie to keep you from doing something worse than lying, by all means DO IT.