I have Googled several keywords within inches of their lives, and can't find the idiom meaning of the expression "a ham with mustard". It's used in the sense of a "ham actor", lousy actor who overplays their scenes, but I can't figure out what it means (if anything) when it comes down to the "with mustard" bit.
It was used in the movie The Story of Vernon and Irene Castle
, as you can see if you scroll down the page a bit.
I'm working in roughly the same era, with a ham-actor sort of character, so I'm very curious.
Mucho thanks in advance for any help ^_^