N-COUNT 调皮捣蛋的人;淘气鬼;小坏蛋 If you call a boy or a man a scallywag, you mean that he behaves badly but you like him, so you find it difficult to be really angry with him. 调皮捣蛋的人;淘气鬼;小坏蛋 [informal, old-fashioned]
It's his idea of a joke, I suppose, the scallywag.