Also:

The invitation had included the word "casual", which he had apparently interpreted as "full suit, except for the tie".

I laughed at that because it is so my personal fanon that Stephen tries to wear a suit everywhere. I even have a never-made-it-into-fic scene for the Needverse where he and Jon are going to be running errands (so, like, grocery shopping and whatnot) and Jon has to threaten to dress him before he puts on casual clothes. Which, considering Jon's fashion choices, was an extremely effective threat. =P