[Yeah, the whole smiling all the time thing might sorta, kinda be Ciel's fault. Look, he was ten at the time, all right? It's not like he's dealt with demons before...how was he to know that Sebastian would read his desires and decide to emulate what he thinks is the perfect guise? Either way, Ciel does find it irksome at times.]
Hazards of being the Phantomhive butler, I'm afraid. And you're a king, no less. I doubt he'll ever show you a less than presentable face.