Duck day is the final day of the working week, usually a Friday. It comes from the saying 'Water off a ducks back' where by the final day of the working week the troubles and concerns that seemed so important and now seemingly less important.
lucy: How was your week
Sarah: I've been working with some terrible customers. Thank godness it's duck day
A duck looks so calm swimming on top of the water but down below he's kicking like mad to stay afloat. A duck day is where your whole team is kicking like mad to keep the stats up or to look good for managers.
Brooke: Thank god your here
Brooke: 2 out sick 1 on leave. It's a duck day.
Beth oh no!