Tell a Lie Day is celebrated on April 4th of each year.
A lie is an intentionally false statement to a person or group made by another person or group who knows it is not wholly the truth. The practice of communicating lies is called lying, and a person who communicates a lie may be termed a liar. Lies may be employed to serve a variety of instrumental, interpersonal, or psychological functions for the individuals who use them. Generally, the term “lie” carries a negative connotation, and depending on the context a person who communicates a lie may be subject to social, legal, religious, or criminal sanctions. In certain situations, however lying is permitted, expected, or even encouraged. Because believing and acting on false information can have serious consequences, scientists and others have attempted to develop reliable methods for distinguishing lies from true statements. (Wikipedia)