There's reason for skepticism, but negative work doesn't seem impossible to me. If you've got a 2 hour status meeting that zaps your motivation, reducing productivity by 50% for the remaining 6 hours of the day, that meeting produced -1 hours of work. (And if you postulate that 32 hours is the limit of productivity for the average employee, those kind of soul-sucking meetings are exactly what you'd expect to be scheduled to fill out the remaining 8.)