My application is much less interesting than various intelligence, special operations, police and others posted here.
I park my truck in the driveway, it is a suburban area with lots of trees and birds. Several years ago a robin or perhaps a gang of robins decided they deplored by truck and any number of times I would see them attacking it with their beaks, especially the reflective surfaces like the rear window. I have no idea what brought on this behaviour, somebody suggested they were attempting to dominate their reflections...
Anyway I didn't care about the beak attacks but either as a side effect or another mode they escalated to chemical warfare and began using my truck as a toilet.
This I did mind, not only for the mess but also because bird feces is acidic and if left can damage clear coat and paint. I tried several home-made and commercial devices to discourage them, none were effective.
The driveway faces a busy road and obviously I didn't want to shoot my own truck, so my options were limited. I ended up sitting on the porch with a sling shot and a bowl of beans or tapioca, these were enough to fly 10-15 yards, not particularly accurate but also not harmful to the truck and not enough energy to leave the property. I don't think I ever made a hit but the startle factor seemed to be enough to drive them off.
This was several summers ago and many robins have come and gone since then with no interest in my truck.
But the slingshot and jar of ammo is sitting on the hall table if the problem resurfaces.