Really? "rub a dub dub thanks for the grub" has to be the worst translation of itadakimasu I've ever heard. Why not just write "thanks for the food" that every manga/anime I've ever seen uses, or the literal "I receive gratefully"? You can say itadakimasu in any setting, from a private home to a michelin-star restaurant, but not "thanks for the grub".
If they said a less formal phrase instead, it might've been an appropriate translation, but they didn't.
