From "Oh what a tangled web we weave when first we practice to deceive!" and used as a put down when you discover that you have been lied to or someone has tried to deceive you.
You: I meant to, but...; Honestly.... ;It wasn't me, the devil made me do it; you don't understand - I had to do it; you wouldn't let me if I had asked; you said no, but I wanted to anyway so....
Me: Yeah right! OWATWWWWFWPTD