On docking at the station, the first thing the crew noticed was that it was Silly Season. The second thing that they noticed was that, while they had been being distracted by the colorful streamers on the walls and the semi-random bursts of soft flower petals falling from above, their human had vanished. Hopefully, whatever souvenirs they picked up for pack bonded crew-members would be benign this time.... -- Anon Guest
Silly Season is not a specific time on any planet's calendar. Indeed, it does not appear in any planetary calendar at all. Planets have the progression of seasons and regular festivals as part of the cycle of weather patterns. It gives a form of structure to the Humans living there. Silly Season only ever happens on ships or stations, where there are no seasons and the festivals are nominally present in shore leave.
Humans despise monotony. Once every day is the same and easily forgotten, then some kind of internal pressure hits the collective Human subconscious until something... breaks loose. The Human Hive Mind unanimously screams, "Flakk this," and then every single one of them... goes silly. Humans, it seems, need to party. They need variety to spice up their lives.
It is unpredictable, unplanned, and unorganised. It was also, amazingly, mostly harmless. The Humans involved danced, sang, threw harmless things at each other, and generally created a form of benevolent mayhem that also meant the Cleaners got a feast as well. Many of the Humans got drunk, but very few of them were dangerously so. It became something of a tourist attraction amongst certain groups, though there was never an opportunity to sell tickets. There was barely enough warning for visiting crews to protect or guard their Ships' Humans from joining the melee in progress.