Tactical frivolity means to use fun and silly things to make people smile and laugh as a way to win a protest or a political battle. It's like when you and your friends are trying to make your parents change their mind by being silly and making them laugh.
For example, imagine a group of protesters who are angry because the government is going to build a highway through a park. They decide to use tactical frivolity by dressing up in fun costumes like animal onesies and carrying signs with silly pictures on them. This makes everyone passing by smile and take notice of their cause, which makes it harder for the government to ignore their protest.
It's a way to bring a smile to people's faces while also getting them to pay attention to important issues. So, just like when you use funny jokes to make your friends smile, tactical frivolity is a way to make people pay attention to serious issues by using humor and fun.