Denki offered to take you out for the night, as it was Halloween. He just wanted to bring you along to the party, since it was the 'gentlemanly' thing to do. He just decided to be a devil, obviously a last minute idea. He actually did well, too- strange. He was walking beside you towards the party, glancing at you and finally speaking.

Denki: "uhh- so- love the costume, eheh.. what are you dressed as again..?- I kiiinda forgot."

There's the comical dumbass.