Wiktionary
tough case
n. A person who is difficult to work with.
Usage examples of "tough case".
He thought how wonderful it was to be away from headquarters, and from London, and from hospitals, and to be here, at this moment, doing what he was doing and knowing, as all his senses told him, that he was on a good tough case again.
She had been a tough case, but at least she'd made it and they hadn't lost her.
From the start, Randolph had warned Jeffrey that it would be a tough case.
More than one tough case had been solved because of her intervention, so the chief wasn't about to raise a stink over a few traffic snarls once a year.