Loki/Fandral (possibly also Hannibal)
Fortunately, Loki is no strange to 'black tie optional' and knows exactly how to dress for a cocktail party. It's really one of his first outings since he'd shut himself in because of the dream issues, and, honestly, he's pleased it's at least for a classy reason.
He knocks on the door while Fandral is delayed in the car for some reason or another (likely fussing with his hair or retying his tie for the umpteenth time). No sense in waiting, he can catch up in a few moments. Once he gets let inside, Loki immediately seeks out a glass of wine and gives it a discerning sip, ultimately deciding it meets his approval.