National Lazy Day is celebrated on August 10th of each year. The staff at National Whatever Day was unable to discover the origin of National Lazy Day. However, it may have something to do with the programming language theory, lazy evaluation.
In programming language theory, lazy evaluation or call-by-need is an evaluation strategy which delays the evaluation of an expression until its value is needed (non-strict evaluation) and which also avoids repeated evaluations (sharing). The sharing can reduce the running time of certain functions by an exponential factor over other non-strict evaluation strategies, such as call-by-name.
National Lazy Day may have also been created simply to celebrate the lazy days of summer.