The ability to fit an XKCD to every situation, and Google out the link to it in a few seconds.
"So Alice encrypts her message and sends it to Bob..."
"You mean like xkcd.com/177/ ?"
Her status message was
"I'd like to make myself believe
That planet Earth turns slowly
It's hard to say that I'd rather stay
Awake when I'm asleep
'Cause everything is never as it seems"
and I immediately thought of xkcd.com/162/