I remember when I was a kid, watching this movie where a boy is put to bed, and he makes his mom check the closet. When she leaves the closet door opens, and a monster steps out. The boy shoots the monster with a ping-pong-ball-gun (remember those) and the monster starts crying. HAHA, does anybody know what this movie is?
The only things I can remember is "Cameron's Closet" and "Monster In The Closet", but I don't think it will be either. What you saw might be from a TV Series like "Amazing Stories" - The Greibble or something.
A horror or science fiction show is a good idea for this. "Monsters" and "Tales from the Darkside" are also possible candidates.
I'm leaning toward "Monsters" myself Andrew as I know it's not "Monster in the Closet" or "Cameron's Closet."
"Little Monsters" is a possibility http://www.imdb.com/title/tt0097758/
I haven't seen it since I was very young and doubt it's on DVD.
Things I remember about it:
The main character is being picked on by a bully at school.
The monster helps him for some reason.
Bully has juice swapped with pee.