The casual gods entered the modern pantheon as people started dressing up for day to day work. As people were forced to wear
pompous,
starched, or
constraining clothing a collective desire was born to occasionally be able to wear something that wasn't quite as stifling.
Thus, the casual gods were born. Being new in the modern pantheon of gods, the casual gods got things a bit off and created masquerade balls at during which nobility would dress up in even more pompous and constraining clothing.
After a century or two, the casual gods inspired a prophet - that of General Mufti. General Mufti (as the legend goes) looked to improve poor morale in the British Army by allowing his troops to wear civilian clothing rather than uniforms some days of the year. Apparently, this tradition as "Mufti day" still is held in the United Kingdom and the Asia - Pacific portion of the world (places where the British Army was). As part of the Mufti day, those dressing up (or down) would give money to a charity in homage to the casual gods.
As part of its transition into the Americas, the casual gods were very successful - especially in that region known as the valley of silicon. While many worship the casual gods on a daily basis, there are some places that require a more formal attire. Here, every Friday has become a "casual Friday", however the charity aspect has been lost in the transition and thus only lip-service is paid to these modern deities.
Casual gods day of worship is casual Friday. Dress ranges from business casual (pantsuits for women in often in a neutral color to a sports coat or slacks, khakis or Dockers for men) to teeshirt, shorts, and sandals. There are tales of individuals showing up on Friday very casual - wearing nothing at all. The priesthood of the casual gods in America is the group known as "human resources" who occasionally try to do something that seems morale boosting.
The casual gods have extended their influence to create a temple of their own known as "TGIF", named after the prayers to the casual gods just before the weekend.