Brooklyn performance artist Freddy (Sebastián Silva) wants to have a child with his best friend Polly (Kristen Wiig), but when his sperm count is found to be low, they convince Freddy’s boyfriend Mo (Tunde Adebimpe) to be the father instead. Silva — also the film’s writer/director — follows the trio’s evolving relationship in a slice of modern city life that takes a dark left turn in its 11th hour.

Wiig and Adebimpe give appealing, naturalistic performances — it’s Silva’s character who grates, especially as he plans an installation featuring himself as an adult baby.

Freddy and Mo’s lives are periodically interrupted by an older neighbor (Reg E. Cathey) whose erratic behavior becomes increasingly menacing. Their mutual antipathy, a microcosm of the borough’s runaway gentrification, is the most engaging part of “Nasty Baby,” but it’s not enough to keep the otherwise rambling narrative together.