The point was, the person spraying it into someone else's face can be held liable on criminal charges for misuse of the pesticide, a poison, which is a federal offense.
And what agency would be the prosecuting agency for said offense? Some lines of defense come to mind. The first would be that doctors prescribe drugs "off-label" on a regular basis without consequence. The second would be that the label said it was effective against pests and the ******* in question was certainly being a pest. Finally, if the entire incident can be characterized as "self-defense", then the tool used during the incident is really not the issue.