VIEWERS of “Late Night with Conan O’Brien” in LA never saw the show’s “Celebrity Douchebag” bit Monday night.

KNBC interrupted the skit – which features colliding model trains – because it feared it might offend viewers still traumatized by the train collision in Chatsworth, Calif. that killed 25 people earlier this month.

O’Brien’s comedy routine featured two model trains – one with a photo of Criss Angel and the other with a photo of “The Hills” jerk Spencer Pratt – colliding and bursting into flames.

That’s what “Late Night” viewers saw in New York and elsewhere.

But in LA, just as O’Brien was introducing the skit, KNBC suddenly cut to a local news anchorwoman.

“We’ll be going back to Conan in just a couple of minutes,” she said.

“Right now in New York, though, Conan is doing a comedy routine about trains crashing – and we feel with our recent train collision . . . it is just not appropriate for us to show it.”

A KNBC spokeswoman said yesterday the station received “a handful” of viewer e-mails that were “mixed” in their comments about missing the sketch.