I've had almost the same exact experience in Paris very recently, and my unforgivable sin was to start by saying : "Good morning, I'm very sorry but I don't speak French. Do you..." I got cut off at this point before I could say the rest. ( ...know where I have to go to buy a HS train ticket ? )

The lady scolded me in French for a couple of minutes after which she got up and left the information desk, leaving me and everyone else behind me scratching our heads.