Gigglemug

Most of the words on a list of old insults are insults. This one mostly is not.

A gigglemug, in the only period source that records it, is not a person at all. J. Redding Ware's Passing English of the Victorian Era (1909) files it under street slang and defines it in four words: an habitually smiling face.

The mug is the face — slang that had been doing that job for a long time before Ware wrote anything down. So the word is built exactly like a caricature: take the face, and name it after the one expression it never drops.

From there it is a short step to the person wearing it, and that is how the word travels now: someone who is always smiling. Nothing wrong with that. It is just worth knowing that the Victorians, as far as the record goes, were describing the face.

Whether it stings depends on the smile. A face that is always smiling can be good company or it can be exhausting, and gigglemug manages to cover both without deciding. That ambiguity is probably why it is the word on these lists people most want to use on someone they like.