I guess Red Tea is no different to any other customer service based establishment in the world in that you occasionally get someone that for whatever reason, isn't at their happiest. People are only human and double bookings happen. And who knows what sort of day this girl has had. She may have just finished with a not very nice customer. As you said, maybe it was just a once off. If not, then do what customers do of other places that provide poor service do and let your feet do the talking and don't return.