When there is an urgent task at hand i.e. a report to finish by the end of the day, but instead you decide to climb into bed for a quick rest - claiming only to be a few minutes; normally around 3pm.
Preferably the sheets will be "fresh" (i.e. washed within the past few days with at least 5 times the requirement of soap and fabric conditioner), with pillows that have been plumped.
Normally "cheeky sheets" turns out be a full "deep sleep" / "REM sleep" / "delta waves". The individual will then wake around 11pm, disorientated, realising cheeky sheets has actually become wholesome deep sleep.
N: don't you have to hand in your report by 4pm?
T: ive got 2 hours its fine, bit of cheeky sheets
- climbs into bed, pulling the covers up to eye level and wrapping around in them
T: ahhhhhhhh cheeky sheets!
-------------------------- 7 hours later
T: ERGH! my report... oh well, cheeky sheets..