"Chew the scenery" explained

Chew (up the) scenery means 'to act melodramatically; overact'. Usually, it's in the context of a play or movie, but it can refer to an aunt of yours who is a frustrated actress. The connotation, either positive or negative, depends on whether the overacting is appropriate to the role or occasion...

Brewer's Dictionary of Phrase and Fable and a couple of other sources attribute chew the scenery to Dorothy Parker, the writer and humorist. In a 1930 review she wrote: "...more glutton than artist...he commences to chew up the scenery." But Random House Historical Dictionary of American Slang has a much earlier (1894) example from Coeur D'Alene, by Idahoan novelist Mary Hallock Foote... The relevant part is about a miner, Jack Darcie, described as being of Scottish family and English education, a young gentleman of prepossessing appearance. After Darcie's entanglements with Faith, daughter of the mining company manager, people gossip about him in a negative light: "Lads, did ye hear him chewin' the scenery, giving' himself away like a play-actor?.."

That information comes from what looks like an interesting website - a Glossary of Theater Terms, where you can look up break a leg, ghost light, the bastard prompt corner, and other familiar or obscure terms.