(all) sweetness and light

Kind and agreeable. Susan's all sweetness and light, I'm sure she's not mad at you.

Cliché very kind, innocent, and helpful. She was mad at first, but after a while, she was all sweetness and light. At the reception, the whole family was all sweetness and light, but they argued and fought after the guests left.

Ostentatious amiability and friendliness, as in One day she has a temper tantrum, the next day she's all sweetness and light. This phrase was coined by Jonathan Swift in his Battle of the Books (1704), where it referred literally to the products of bees: honey and light from beeswax candles. But in Matthew Arnold's Culture and Anarchy (1869), the term meant "beauty and intelligence." In the 20th century, however, it was applied to personal qualities of friendliness and courtesy and to the general pleasantness of a situation, as in Working with him isn't all sweetness and light, you know. Today it is generally used ironically, indicating lack of trust in a person's seeming friendliness or for a difficult situation.

Saccharine goodness and cheerfulness. Originally this term was used in all seriousness by Jonathan Swift (Battle of the Books, 1697) for the two products of bees, honey and wax (for candles), and by Matthew Arnold (Culture and Anarchy, 1869) for beauty and intelligence. It was the latter that led to its widespread adoption. Today, however, it is always used ironically, as in, “‘This one’s on Thames House.’ ‘That’s very generous of them,’ said Goss drily. ‘You know us. Sweetness and light’” (Stella Rimington, At Risk, 2004).