Is it bad to be sprayed by a fire extinguisher?

Answer 1

If it belongs to someone else and you're doing it without permission, yes; if it belongs to you, then "stupid" is probably a more apt term for it. There's not a great deal of fun to be had in playing with the now-ubiquitous dry chemical types anyway. Anecdote: many universities require graduate students in chemistry to take a fire safety class. In one I took, the instructor told us that they used to have the old brass pump-style water fire extinguishers in the dorms; they would occasionally during an inspection find one that had been filled with beer as a sort of impromptu keg. The good news was that beer would at least still put out a fire. When they discovered one that had been filled with gasoline, though, they removed those and replaced them with carbon dioxide extinguishers. However, they found those frequently needed recharging: students had discovered you could chill a can of beer quickly by sticking it in the horn and setting off the extinguisher for a second. They were in the process of replacing those with dry chemical extinguishers; in the words of the fire safety instructor, "The students haven't yet found any way to do anything with those except make a mess, which they have to clean up, so they don't get tampered with much."

Answer 2

The chemicals in a fire extinguisher will normally not hurt you in an open area (remember some displace the oxygen to put out the fire.) However the danger comes when someone plays with a fire extinguisher and puts it back with out recharging it so it can NOT be used in an emergency. Fire extinguishers are not toys and should be handled only in an emergency.