Assumptive

To constantly be assuming, to take for granted, to make an ass out of you and me

Everyone was assumptive over that odd lady, and they stole her car to see what she has.
They were assumptive over one’s office, so they broke in at night to see what the worker was doing, looking at his computer.

One student was assumptive the teacher was hiding test answers, so he broke in to see if he was right.