The argument was that it was unfair that atheists had no recognized days for their religion as other religions did. 
The case was brought before a judge. 
After listening to the passionate presentation by the lawyer, the judge
 banged his gavel declaring, “Case dismissed.'
” The lawyer immediately stood and objected to the ruling saying, “Your 
honor, how can you possibly dismiss this case? 
The Christians have Christmas, Easter, etc. The Jews have Passover, Yom
 Kippur, Rosh Hashanah, and Hanukkah.
 Yet my client and all other atheists have no such holidays.” 

The judge leaned forward in his chair and said, “But you do.
 Your client, counsel, is woefully ignorant.”

The lawyer said, “Your Honor, we are unaware of any special observance
 or holiday for atheists.”

The judge said, “The calendar shows April 1st is April Fools Day, and Psalm 14:1 states: 'The fool hath said in his heart, There is no God.' Thus, it is the opinion of this court, that if your client says there is
 no God, then he is a fool.
 Therefore, April 1st is his day. Court is adjourned.”—Source Unknown