When we speak about other people, we must speak the truth. Lying about the other is also called gossiping. Lying to deliberately harm the other is called a false witness.
We grumble when we are discontent. Sometimes we have a good reason to be unsatisfied. However, often it is with no reason.
Is a little white lie okay? Is there even something like a white lie? We can make things very difficult for ourselves with these questions. God, the One Who is called the Truth, is very clear about lying and deceiving.