Why is lying always wrong?

Of course lying is wrong, its always wrong, even if you really need to. However, by "if you really need to" that doesnt apply to everything, if you hae stolen something that doesnt blong to you, then lying is definatley wrong. But there are those personal lies, such as, if someone comes near the door whilst your masterbating and you dont want to get caught? Well, its not like you gonna say: "dont come in! Im masterbating!" you say like, "oh god please dont come in, iv trumped" or soemthing. I understand that that was a strange answer but im not being sily, im just examplifying. So no reporting please it was just an example.