Tonight, a filmmaker returns to a family so loathsome, it’s funny. Almost. Louis Theroux revisits the peculiarly vengeful Phelps clan in his new documentary “America’s Most Hated Family” (9 p.m., National Geographic). The Phelpses are the family/congregation behind the infamous Westboro Baptist Church, the folks who hold up taunting signs at funerals, “celebrating” those who died and demonstrating their belief that America has become demonic and impure.

A slight, irreverent figure and British to boot, Theroux often resembles John Oliver of “The Daily Show.” Before that series became a source of “news” for millions of younger viewers, it was best known for cruel ambush interviews with the deranged and self-deluded.

The Phelpses are well aware that Theroux is using interviews with them for ironic, if not comic, effect. At the same time, they know that any exposure is good publicity for their reviled cause and microscopic following.

Theroux spends much of the film following up on members he interviewed four years ago for the first “Hated” documentary. And several of those congregants, young women in their 20s, have left the fold. Theroux also interviews these exiles’ parents, who display a chilling indifference to the loss of their daughters, dismissing their departure as choosing hell over salvation. Case closed.

It’s impossible to showcase behavior and beliefs so extreme without tipping over into absurdity. We’re shown some young teens practicing choreography to popular music with the lyrics changed to reflect the Phelps family’s penchant for vicious homophobia. Theroux hangs out with a 7-year-old convinced that “the Anti-Christ lives in the White House” and visits a young woman whose room is painted with tidal waves to rejoice in the deaths of sinners claimed by recent tsunamis.

One particularly astringent Phelps woman is the spitting image of Jane Lynch’s grandmother character in “Talladega Nights.” Given so much weird material, I wouldn’t be surprised if somebody turns the Phelps family into a sitcom. Or at least a reality show. Many of the family’s followers already seem camera-savvy. And in Theroux’s hands, they’ve become the Kardashians of intolerance.

• Actress Anna Deavere Smith embodies a parade of different characters discussing issues of declining health, life and death in the “Great Performances” (8 p.m., PBS) presentation “Let Me Down Easy.”

Tonight’s other highlights

• A major rift on “A Gifted Man” (7 p.m., CBS).

• Bo Derek guest-stars on “Chuck” (7 p.m., NBC).

• Bruised feelings in the Peach State on “Kitchen Nightmares” (7 p.m., Fox).

• Victims become suspects on “CSI: NY” (8 p.m., CBS).

• An escaped fugitive exhibits remarkable powers on “Grimm” (8 p.m., NBC).

• Peter crosses to the other side to confront a parallel Walter on “Fringe” (8 p.m., Fox).

• Doug and Claire can’t live without “Battlestar Galactica” on “Portlandia” (9 p.m., IFC).