As if!

as if

1. Like. I have such a terrible headache—I feel as if my head is going to explode. I did tell her that I wouldn't be home for dinner tonight. It's as if she doesn't listen to me at all!
2. An interjection indicating complete dismissal of what has been said or suggested, implying that it is not the case or would never happen. A: "Tim thinks he's going to go to the prom with you." B: "As if! I'd rather go by myself."
See also: if

as if!

used to express the speaker's belief that something is very doubtful or unlikely. informal

As if!

and AI
exclam. an expression said when someone says something that is not true but wishes that it were. (Also, and perhaps usually, sarcastic.) A: I’ve got a whole lot of good qualities. B: AI! My hair should look like a pile of wet thatch? As if!