as if/as though
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."
Similar to, likened to, or fashioned after something like it were the truth. So many bad things happened all at once, it's as though life itself were against me. He acts as though he's some famous author, though really he's only ever published a single short story.
See also: though
Also, as though. As it would be, as in He decided to accept, as if it really mattered, or John scowled as though he were really angry. The first idiom dates from the late 1500s, the variant from the late 1700s. Also see make as if.