Mid-Autumn Moon Festival
Mid-Autumn Moon Festival is 中秋節, zhong qiu jie celebrated annually by appreciating the moon at its most luminous on earth (also known in American folklore as the Harvest Moon) with family and friends eating mooncakes and looking at the moon.
And while it is not an explicit tea holiday, sitting outside and staring at the moon with family and friends while eating mooncakes seems like THE PERFECT opportunity to also sip tea together.