She thinks he doesn't do his share of the housework, while he says things are even steven.
"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).