BPG24 said:
3 or 4 drops of Visene in a soda is one hell of a good April fools day joke...
give it a try
Please Do Not Try This!
http://theurbansherpa.com/blog/permalink.php?id=106
Visine is, in fact, toxic. Its active ingredient is Tetrahydrozoline, a substance which, even in small doses, has caused nausea, vomiting, dangerously low blood pressure, dangerously low body temperature, and comas. The makers of Visine (Pfizer) are very clear: "If swallowed, get medical help or contact a Poison Control Center right away."
The Internet is rife with stories of practical jokesters slipping Visine into people's drinks, because, the story goes, ingesting it causes sudden diarrhea. According to Snopes, diarrhea is one of the few side effects you won't get from Visine.
If you are trying to give someone the runs, my advice is stick to good, old-fashioned, ground-up Exlax: it's safer and has an almost-pleasant chocolatey taste. It mixes well with brownies, cake, and Coca Cola. Perhaps more to the point, please remember that
secreting noxious substances into food and drink for the purpose of bringing harm to others is called poisoning, and most states, it's a felony offense.