A few comedies ( I believe wedding crashers) show a character putting a few drops of visine in someones drink to give them severe diarrhea. I had wondered at one point, if that works so well, why isn't it prescribed for constipation, or as a prep? Up until recently I hadn't found my answer. Even though I am a D gal instead of a C gal I had wondered if a drop or two could help you constipated crohnies. And then I found this article.
http://www.snopes.com/medical/myths/visine.asp
It actually doesn't cause diarrhea and is VERY DANGEROUS to ingest. I can't help but think it is irresponsible of movies to show it being used in this way if it is not how it works and so dangerous if attempted.
So, point being, no matter how bad you want to poop, don't drink your visine.