"You missed one, here." With my pen, I indicated the box still awaiting his signature.
"Ahh, sheesh," he said, with a sheepish shake of his head. "I'm still not all the way awake today!"
It was 3:30 in the afternoon.
"Dude...it's okay. No need to save face. You're as awake as you'll ever be. You just made a simple mistake. An oversight that happens to everyone. It's not a weakness or a disadvantage. Hell, if you think about it, the awkward excuse actually makes you look sillier than a momentary lapse of attention! Isn't it funny how complicated we make social interactions just to avoid being seen too clearly? What are we really afraid of? But it's all good. Everything's all right. Smile and enjoy this beautiful day."
Of course I didn't actually say that. I played my part in the social script. Just a sympathetic "heh" and a nod. Too much honesty's liable to get you an ass-kicking. Look away, pretend you didn't see any vulnerability.