I'm thinking of putting chemicals in one of the women's hair at the picnic.
Why are you thinking?
I think it might be a good thing to do.
It is wrong to harm someone and possibly give them severe burns on their head. It is a crime to put chemicals on people for whatever reason with out their consent.
It will be funny.
Unless you're her hairdresser dying her hair the color she requested, you have no right to put anything in her hair. It would be considered an assault and you'd expose yourself to a lawsuit, arrest, or both.