I used to feed birds on the fireplace at this apartment I had, and used to put ground cayenne pepper to dissuade the squirrels from eating it all.
Twice, as I was doing it, a gust of wind blew it straight at my face.
Ouuuuuuuuuuuuuuuch.
Paper bag + cayenne + firecrackers + match = instant tear gas in case of emergency.