Congratulations on Applying Archaic Units of Measurement Unhelpfully!

When she asks you how far it is to town, you'll answer her in leagues.

"Like, groups of baseball teams?"

She was never the brightest, but in this case, her criticism will be reasonable - you won't have used the archaic measurement (which we'll charitably presume to be about overland distance) correctly.  You'll have told her it's "a thousand leagues," which is like, three thousand miles.  The town will be about a twenty minute drive away.

"Do we have enough gas to make it?" she'll ask.

"We've got a half dram," you'll say before running your hand through your hair.  "We should be good."

She'll cock her head at you, puzzled.  She'll know the term dram from her time as a professional whiskey taster, but she'll also know that it means "a small amount," literally a sixteenth of an ounce.  She'll say that to you, and you'll laugh at her.

"God, you've a brain much as a half-stone."

At first she'll think you're telling her that she's got rocks in her head, which will be offensive on its own, but after a moment she'll realize you mean the old measurement.  That one, she'll know, and it'll be pretty close to accurate (half a stone is about seven pounds, close to the weight of the average human brain) but the obtuseness, the dickishness, and the almost happenstantial rightness of what you're saying will all come together and push her towards a singular conclusion.

"I'm leaving you," she'll say before pulling on the e-brake, forcing the car to  stop before stepping out and walking along the road alone in the direction of town.  You'll just sit there watching her as she moves away for minute after minute, down the road away from you.  As you watch her image slowly fade, your fingers will regain feeling, you'll regain the capacity to move inside the car, to manipulate its various levers with your hands, but you won't employ it.  Instead you'll just sit there and try to determine how far she's gone down the road.  The distance will be difficult for you to quantify; you'll lack the words to define it.

Congratulations on Applying Archaic Units of Measurement Unhelpfully!