There is quite the variety of possibilities, out of these possibilities the ecchi life style is quite obvious, since every guy who doesn't think about something like this would be more fitting as the best friend of Vali or would be an angel.
So what would you do?
How would you interact with a certain character?
How would you react in a certain situation?
I hope for many ideas and suggestions, since I like these parts where Issei has a "normal" daily life but it was recently quite short.