Having a snowball fight is illegal in Aspen, Colorado, because the act is a violation of a local anti-missile law. In the city, throwing any object or discharging a weapon at public buildings, at private property or at another person is an infraction that typically comes with a fine as punishment. Snowball fights on private property are generally not cause for issues. In some cases, however, the throwing of snowballs that are made of a significant amount of ice has been treated as assault or harassment and has come with criminal charges.
More about Colorado state laws:
In Denver, Colorado, vacuum cleaners are not permitted to be lent or borrowed.
It is illegal in Boulder, Colorado, for the owner of a llama to allow the animal to graze on public property.
In 2013, Colorado and Washington became the first US states to pass laws for the legalization of marijuana for recreational use, but it still was illegal under US federal law.