There are many many manga things that only make sense if you realize it's aimed at the readers, like gyaru who love otaku. So this is pure Family Guy nobody would actually do this gag stuff. 'Shin's butt stinks and she's really mad about that' is a good recurring gag.I understand why he keeps sniffing her butt, but I don't understand why he keeps sharing that he does. Especially since, as far as we know, it might not even be a useful method of checking her health.