“If you’re trying to break up with me, just man up and do it.”

In a play about an ordinary couple, that might be no more than a mild crack. But in “Plot Points in Our Sexual Development,” which opened on Monday at the Claire Tow Theater, it’s a game changer.

Cecily, the character who angrily flings the line, is a cisgender lesbian. Theo, at whom she flings it, is a self-described “genderqueer trans person who is not a woman and is not a man, but is kind of a man, who loves lesbian jokes.”

Forty minutes into an hourlong work that has, until then, seemed restrained and respectful to the point of tediousness, “man up” comes off as intensely provocative, both on the part of Cecily and on the part of the playwright, Miranda Rose Hall. It’s a phrase that acknowledges the complications of gender and sexuality as they are ever more finely sliced today — but it’s also a challenge to live beyond abstractions.

The play, Ms. Hall’s first professional production, faces a similar challenge. As directed by Margot Bordelon for LCT3, it seems for most of its length to keep present-tense emotion at bay, as if in some kind of exercise or ritual. As the lights rise on the barest of stages — just two chairs, a door and a herringbone parquet — Cecily (Marianne Rendón) and Theo (Jax Jackson) are seated well apart from each other, facing straight ahead.