Wasps and hornets aren’t just annoying, they can be deadly to those who are allergic to them. Short of using nasty pesticides to kill them, you can try to spray them away with water or pepper spray — but be prepared to run if they identify you as the source of their misery. Unfortunately, even if you drive them away they might come back.
One way to arouse their territorial instincts is to hang up an artificial “decoy” wasp nest that will drive them away when they see it; wasps will think it’s an enemy nest. Commercial wasp nest decoys are available, or you can try painting a crumpled paper bag gray and hanging it up where wasps are a problem.