For some time I have been wanting to tell a friend she looks rather like Queen Mary. All she needs is a toque, a long dress, pearls— a great many of them—and a furled parasol but I don’t say this because I don’t think she’d like it and certainly wouldn’t approve of the Queen’s habit of embarrassing her hosts into parting with their prized antiques. And my friend would take a dim view of anyone who collected Fabergé. So that is one conversation, admittedly trivial, which I do not have. Another conversation disallowed is when I’m a guest at dinner…