Example: She thinks he doesn't do his share of the housework, while he says things are even steven.
Origin: "Even steven" is merely modern rhyming slang (like "drop dead, fred", "see ya later alligator", or "know what I mean, jelly bean?").
Rhyming slang is common in many languages and dialects, and is particularly common in cockney English. Cockney rhyming slang takes the idea a bit farther actually substituting a rhyming word or phrase for common terms (e.g. "apple fritter" means "bitter (a type of beer)", "Johnie Horner" means "corner", "Rub-a-dub" means "Pub" and so on).