An imaginary weapon shot at people who fit the description of douche bag. Usually when using a douche dart, people hold up any object they may be carrying and pretend to use it as a gun. Also, douche dart firers must make the best "dart" noise they can.
I saw Trevor walking down the hallway with his hair spiked and I just had to shoot him with a douche dart.
"Hey Kyle, did you see me shoot him with my douche dart?"