It's called forbidden fruit.  Whatever that "fruit" translates to, we've all got something in this life we're not allowed to have.  Whether your doctor tells you that you can no longer eat fried foods, or you're a dog that's been told to stay off the bed, the most delicious fruit is the forbidden variety.

This dog's forbidden fruit is the bed.  He's not allowed on the bed.  Let's not get into the discussion as to why the CAT is allowed on the bed, but not the DOG.  This pooch is careful enough to wait for "mom" to leave the house before going nuts and enjoying that forbidden fruit.