You'd Think it would be Obvious
Scene: Very nervous young woman about to have her first GYN exam.
I talked her all the way through it before she ever disrobed; I was at my most soothing and reassuring. Here's how I finished up my spiel:
Me: And whatever happens, remember to keep breathing.
Her: What happens if I don't?
Me: You'll die.
Of course I began cracking up as I said it, as did she. Tension broken. Laughed for weeks.