The actual meaning behind this acronym is beside the obvious (which is to get the fuck out). It is best used in a situation not unlike that of one where a girl or maybe a friend that the rents hate to leave the house immediately, because they are coming home.
Oh crap! My mom's at the door! She's coming in! I'll hold open this window, you've got to GTFO!!
You: Man, I was so drunk last night. I think I barfed in my purse.
Your buddy: No, that was your pillow case. And you slept on it anyway.
You: GTFO!! Is that why my hair is so sticky?!