> for full effect: say slowly, in one sighing breath, emphasising each word more than the previous, and take a deep disappointed breath after
I tried that and saying the last word made me exhale enough to force me to immediately take a disappointed-sounding breath, so I guess it works as designed?
If you don't feel the final breath feels intentional enough, too much like you are just out of breath, add a head nod. Though I find that sort of exasperation gets the message across better if looking directly at the subject of it.