In a joking way, when you say or do something that makes fun of someone a little — but in a warm way, because you like them. "'Nice haircut,' she said teasingly." The words might sound like a small attack; the tone says the opposite. That gap is the whole point of the word: it tells the reader not to take the line seriously.

So teasingly almost always signals closeness. You tease a friend, a sibling, a partner — not your boss and not a stranger. Because it describes tone of voice, it appears most often next to speaking verbs: said teasingly, asked teasingly, teasingly suggested.

There is a second, quite different use, common in stories and advertising: doing something slowly and only part-way, to make someone want more. A trailer teasingly shows three seconds of a film; someone teasingly holds a gift just out of reach. Here it means "keeping you waiting on purpose".

One honest warning about the friendly sense: whether teasing feels warm or cruel depends entirely on the relationship and the tone. The word claims it was meant kindly. It does not prove it landed that way.