"Did I stutter?" Crowley says. "I don't need you blowing yourself up to save me. You might get some of yourself on my jacket, and that's the sort of stain you can't ever get out."

Cause that, of course, is the reason why Crowley can't fathom the idea of the human soldier person dying for him. He's already certain that if Aziraphale were awake, he'd die for Crowley which is just as unfathomable and horrific. People need to just let Crowley do his own stupid things on his own.