"Romani ite domum" (Romans go home) is the corrected Latin phrase for the graffito "Romanes eunt domus" from a scene in the film Monty Python's Life of Brian.
The scene features John Cleese as a centurion and Graham Chapman as Brian, at that stage a would-be member of the revolutionary group the "People's Front of Judea". To prove himself worthy to be a member of the group, Brian has to daub an anti-Roman slogan on the walls of Governor Pontius Pilate's palace in Jerusalem, under cover of darkness: "Romans go home!", written in Latin so the Romans can understand it. He has just finished when the centurion sees him. Brian is terrified and clearly expects to be killed on the spot. However, upon reading Brian's message and realizing that its grammar is atrocious, the centurion becomes distracted and instead angrily corrects Brian's mistakes.
"What's this, then?" he says. "Romanes eunt domus? 'People called Romanes they go the house'?!" Brian is then forced to remember the correct Latin declension or conjugation for each word as if he were a delinquent school boy. "Now," says Cleese when they eventually get to the correct form, Romani ite domum, "write it out 100 times. If it's not done by sunrise, I'll cut your balls off." Brian does so, covering nearly every surface of the plaza with the phrase, and becomes a hero. In subsequent scenes, various Roman soldiers can be seen erasing the graffiti to censor the seditious message.
"Romanes" is a nonsense word in Latin, hence why the Centurion refers to it as "people called Romanes". The proper plural ending of Romanus is "Romani", as it is a second declension masculine noun. Brian used the 3rd declension plural ending "-es".
As the dialogue explains, Brian used the indicative form of "eunt"—in the third person plural, for "they go"—but he should have used the imperative form of eunt to make a command, which is "ite".
Case of Domus
The exchange on the case of domus concludes:
Students of Latin often note that domi is the locative of domus in literary classical Latin. The case construction used in the final formulation is accusative of motion towards.