The full title of the popular 1940s BBC radio comedy - ITMA.

The title derived from newspaper references to Adolf Hitler. The show became very popular and after a while the 'man' of It's That Man Again came to be thought of as Tommy Handley, the lead actor. The show made heavy use of catchphrases, some of which have been assimilated into the language:

"I don’t mind if I do" (From the comic device where Colonel
Chinstrap invariably turned remarks into offers of a drink.)
"After you, Claude - no, After you Cecil."
"TTFN" (Ta ta for now.)