This expression is a step up in the difficulty from the one in Stellvia. In ep.06 of Sekirei, at 13:50, Tsukiumi says something that sounds, very approximately: "go ni itte wa, go ni ishitebai to moishteno..." (I'm not even going to bother with the hiragana, so imprecise it is). The translation is, "when in Rome, speak like a Roman". The "~to moishiteno" is obviously a very corrupted "as they say" or "as the saying goes". Therefore "go ni itte" is probably "As you go to Go", and "go ni ishitebai" may be a mis-heard "go ni shiteba ii": "good if do as Go". I have no idea what Go is and not even sure if it's long Gou.

P.S. Another useful thing I learned was, room #203 is not called "二百三度", but "にまるさんど". Kind of like Americans say "two-oh-three".

UPDATE: Matthew sagematt@#animeblogger says it's "郷に入っては郷に従え" (ごうに いっては ごうに したがえ). It's actually on the page for "gou".