Formal Friday is the tradition, practice even religion of wearing a suit every friday regardless of what the dress code. It is specially more effective if they have casual friday. I started about 7 years ago after being told that I could not wear black jeans to work on Friday where they had business casual dress code. So now I wear a suit every Friday and I have a few of my friends and co workers do the same.
Why are you wearing a suit on a Friday?
It's Formal Friday. F'n Friday.
Nice suit but it's Friday?
Yes, It's Formal Friday. F'n Friday.
You're wearing a suit on Friday, do you have an interview?
No, It's Formal Friday. F'n Friday.