Sam Rockwell took his role as a flustered science teacher a little too seriously on “Saturday Night Live.”

The Golden Globe-winning actor dropped an f-bomb during a failed attempt to inspire two young students to learn about the density of oil and water during his first sketch as host Saturday night.

“Just pour the oil into the water. The oil is ... Josh, you can’t be f--king this stupid,” Rockwell blurted out. “Sorry. Kids aren’t stupid. Just say what you see. Just look at it.”