‘NAPOLEON Dynamite” star Jon Heder, above, is slipping back into his nerd boots to guest star on “Mad TV” Saturday night.

In a rare TV appearance, Heder joins singer Alanis Morissette on the show, including a parody of a Gatorade commercial.

For the phony energy drink spot, Heder plays the captain of a high school math club who are losing a competition against another group of math nerds.

“It’s in black and white and they start sweating in those iridescent colors,” says executive producer Dick Blasucci. “I wanted him to play a little of the Napoleon Dynamite kind of guy without going all the way and still give the audience what they want to see [him as] with that kind of character.”

Heder starred in last summer’s cult hit movie about an alienated, small town teen with a bizarre home life who tries to help his new friend win the class presidency.