Also Kodomo No Jikan might qualify in my opinion, the girls tease their profesor with their casual attitude, and there is a lot of casualness in the Touhou anime series, must be their custom in Gensokyo! And there a a lot of casual scenes scattered thru many anime and hentai-animes like Imouto Jiru. I guess you can also watch Kanokon and KissXSis! A notable mention is also Queen's Blade, and don't forget the Pokemon beach episode!