The best concoction for misting/spraying from the mouth that I'm aware of is used by carnies and rasslers. Here's a vid of Tajiri using it:
http://www.youtube.com/watch?v=tfqwrQpOhls
The liquid is kept in candy wax and doesn't keep for very long so it is a home brew. The longer you intend to have it, the more wax you'll use. Luckily the wax doesn't break down any faster in the mouth than when stored on you. Once used, smaller capsules can be swallowed immediately. Larger capsules usually get shoved between the gum line and cheek.
To get bright colors like the almost neon green that Tajiri used in the vid requires an ingredient that tastes terrible. You can use a soy base for normal tinted primary colors that is neutral in taste. Both methods will permanently stain natural fibers as well as temporarily stain your tongue.
As for the way that Tajiri used it, it's a lil' more versatile than how his use came across. Tajiri's gimmick is that he can't speak English. He could have talked all the way up to spraying id he wanted. He also does this weird thing with thumbing his cheek before and after the spraying. AFAIK, this is just a mannerism of his and does nothing in regards to breaking or delivering.
You can thicken the recipe by adding corn starch but that's a common ingredient in the prank/Halloween type stores. If that's the kind of density that you want then it's cheaper and easier to just buy from the store.