The Mikado is rather an evil laugher...
The tradition of a loud, long laugh in the Mikado's song began in the 1930s, I think. This is a good moment to remind everyone that my favourite film - Topsy-Turvy - is on BBC2, 11.15pm on Sunday. It shows how the Mikado came to be written and performed and they do stick very well to the facts. When the Mikado's song is sung (it was almost cut for the first night) sure enough there is no theatrical laugh.
There are many examples of laughing in the songs in G&S but perhaps the best examples are the "Paradox" song from
Pirates and "I once was as meek" and "The ghost's high noon" from
Ruddigore.