not put it past
not put it past someone
to think that someone would not dare to do something. He might run away from school. I wouldn't put it past him. I wouldn't put it past Roger to arrive unannounced.
not put it past somebody
to not be surprised if someone does something unacceptable Jenny wouldn't put it past Jess to turn Lester in to the FBI and claim the reward. She had a great imagination, and I wouldn't put it past her to make the whole matter up.