I've been trying to figure out where this moment is from for the longest time and I'm coming up short. All I can recall (I saw this when I was a kid) is that it was a horror story about a kid complaining ot his parents about a monster in his closet and they wouldn't believe him. Don't really remember much else about it except that the very end has the mother cleaning up the kid's room and when she looks over at the closet there's this big white hairy beast thing with red eyes that lashes out at her and then its over. Scared the hell out of me as a kid but I cant find what its from. Could be Tales from the Darkside for all I know. Can anyone help?

This is a bit of a wild guess as I don't remember how it ended, but the movie that came to my mind from your description was Cameron's Closet.

http://www.rottentomatoes.com/m/camerons_closet/