From H.K. in Canada:
One Saturday afternoon several years ago, a male patron came into the library (we are an academic library) asking for access to the internet (we often give out temporary passes to visitors). His only identification was his prison inmate ID card! This was the first red flag.
He went up to the second floor and proceeded to watch poronography at one of the computer terminals. A female student came down to the circulation desk and complained about it. My coworker went upstairs to verify, and he was indeed watching porn and masturbating under the table. We then called security who went upstairs to remove him. When they approached him he said, "Wait til I'm finished."
Security dragged him out anyway, thank God. He was not happy.