You would probably not say that he was sleeping the sleep of the just, unless you meant the just asleep, but it was certainly the sleep of someone who was not fooling about when he climbed into bed of a night and turned off the light.
The anxiety children feel at constantly being tested, their fear of failure, punishment, and disgrace, severely reduces their ability both to perceive and to remember, and drives them away from the material being studied into strategies for fooling teachers into thinking they know what they really don't know.john holt
It takes all sorts of in and outdoor schooling To get adapted to my kind of fooling.robert frost
Few poets have made a more interesting rhetoric out of just fooling around: turning things upside down, looking at them from under the sofa, considering them (and their observer) curiously enough to make the reader protest, “That were to consider it too curiously.”Randall Jarrell
Hurry up, you Hoosier bastard, I could kill ten men while you're fooling about!.