Lemon Monday
The poor sour look on co-workers faces (as if sucking a lemon) when something or someone has ruined their day. This condition is highly infectious and seems to be more common on Mondays but there is also a high incidence of Lemon Wednesdays especially in the cold dark days of winter.
After observing several employees with this condition, the manager will exclaim, "well it's official, today is Lemon Monday, feel free to express yourself accordingly".