Is wasp spray legal in Washington state for self defense?

Answer 1

That's going to be evaluated on a case-by-case basis. You're essentially using a chemical weapon, and one which will have harmful effects if ingested, so there's a strong possibility it will be treated as a use of potentially lethal force, and you would likely face felony charges if your use of it wasn't determined to be appropriate to the threat you were contending and the conditions requires for lethal force to be used legally.