C'est vous qui le dites.

15. C'est vous qui le dites.
pronounced more or less: say voo key leuh deet
Literal translation: It is you who it says.
Variant: C'est toi qui le dis.
Meaning: That's what you say. / So you say.
Implications: C'est vous qui le dites immediately calls into question the validity of the comment just made and the honor of the person who made it. It expresses disagreement, is not necessarily accompanied by any explanation and attempts to put the other on the defensive by implying: "I disagree with you, so you must be wrong. What do you have to say about that?"
Remark: Yes indeed, the French do have sundry ways of letting you know that you don't. Stump them by asking if this is strictly French or is it a cross-culture tendency.

Example: Friends and acquaintances are chatting (in French) on the village square one balmy summer evening. The conversation turns to the upcoming soccer match between France and Germany. You say you're looking forward to it. Laughter. Implication: How could an American be interested in soccer? After all it's a European sport, not American.

OK, sure, soccer may not be as popular in the US as in France, but has been growing steadily since the 80s. More and more American kids are playing it and many American cities have professional teams. You politely explain this then add: "My son grew up playing soccer. In fact, I grew up playing soccer." You should definitely know whether you and your son played soccer, right? That can't possibly be called into question, right? Yet you incredulously hear a guy utter, "C'est vous qui le dites." So what's he expecting, for you to grab a soccer ball and do a David Beckham imitation? In all fairness, he may be referring to the first part of what you said, but either way...franchement. Dance him around the square singing, "C'est moi, c'est moi, 'tis I." He won't get that either.