In BDSM, D/s code phrase for, "Are you in your role?" A Dominant will ask his submissive this just before a scene. If the sub needs a few minutes more, this is the time for him/her to mention it. If the sub's answer "Yes, Sir/Mistress" then the scene is on.
Dom: "I'm coming by in 20 minutes with a friend. Same as last time: take your top off; on your knees; him first, then me. Do not speak unless you're spoken to. Are you ready?"
This question arises from people who are interested in selling you drugs, connecting you with prostitutes, or simply ripping you off if you are dumb enough to give them cash for drugs before seeing the product.
Used by thugs, people in the 'hood, and scam artists.
Thug: "Are you straight, man?"
You: "Lookin' for a dub ($20 rock of crack)."
When something is so unbelievable that the phrase "are you shitting me?" is not enough. It demonstrates that the action taking place, or the event being described is so monstrously horrific that it literally feels like someone is taking a massive shit inside of your chest. Basically, the worst feeling ever is happening, and at this point you're questioning why the fuck.
Douche: LOL I TOTALLY RAPED THIS CHILD WITH A PITCHFORK OF AIDS
Person: ...are you shitting inside of me?
Douche: ...No? But I could be.