Yeah, "you are now breathing" manually is pretty evil, but what about "you are now blinking manually"? I feel like that would be just as if not a bit more annoying. However, you could also curse someone with "you are now swallowing manually" which is just a whole other level of uncomfortable/annoying.
HOWEVER, you could also use all three at once to inflict maximum damage! For example: You are now breathing, blinking, and swallowing manually. Have fun!