Well, at least somebody remembered about casual Good Friday.
A playful combination of the phrases "Good Friday" and "casual Friday". "Good Friday" is a christian holiday that takes place close to Easter, as represented by the Easter bunny costume. Casual Friday is a common office policy that encourages people to wear less formal clothes to the office, which the Easter bunny costume would be. So, on casual Good Friday, an Easter bunny outfit being worn to work would be appropriate.