Ranbir Kapoor, Katrina Kaif caught in a lovers' tiff?

Ranbir Kapoor and Katrina Kaif`s alleged relationship has been the talk of the town, ever since Kareena Kapoor addressed Kaif as her `sister in law` in a chat show. The star couple, who reportedly went on a vacation together to celebrate the New Year, are said to be at loggerheads with each other.