The person doing the spraying knows it’s just a water pistol. The person being sprayed has just been exposed to an unknown liquid by an unknown person. Considering this is also how acid attacks work, it’s not really that cool of a thing to do to people.

Sounds kinda similar to how Wikipedia was approached by instructors. I remember an English teacher proudly proclaiming she had participated in a “Kill Wikipedia” seminar at a convention. Just a few years later, they’re instructing students on how to properly use Wikipedia as a starting point and not a primary source.