1. To tinker or fiddle with something inappropriately, especially as to cause it to stop working properly, whether due to malice or ineptitude. With screwing with my computer, you're going to break it! I think someone screwed with the control terminal, because none of these buttons are working right anymore.

2. To trick, deceive, confuse, or puzzle someone. He's so gullible that all the kids in his class like to screw with him. One minute she's flirting with me, and the next, she's completely disinterested. Her mixed signals are totally screwing with me! Don't screw with me, Tom—you try any funny business, and I'll make you regret it.