I agree with John regarding certain snake's individual attitudes. It is definitely disheartening, but sometimes no matter how hard you try there are some reptiles that just are completely intractable.

However, that doesn't mean that you still shouldn't try to develop some sort of trust between you two, and maybe things will calm down in the future. I have had snakes that have never even struck at me, and some that were unbelievably aggressive.

I recommend getting some type of work gloves to wear when ha fling the snake. Reduces your flinching when struck at, and has seemed to work for me in the past.

One thing to keep in mind is that if you have breeding age males in with females, there is always the chance that the male is getting hormonally revved up when in proximity to females. I've noticed that my males get extra ornery this time of year. We usually see that respond in burms and retics, but it's just as plausible for boas.