Go to http://www.snopes.com/.../redbull.htm. If you get any customers asking about Red Bulls safety youll know how to allay their fears.
The snopes site has this to say about the rumour:
What we have here is yet another baseless scare associated with a popular product. The Internet makes passing along such wild bits of scaremongering as easy as hitting a key on a keyboard, and because of this, ludicrous 'facts' about popular products leap from inbox to inbox in less than the blink of an eye. It's reckless gossip of the high-speed variety, and it can prove exceedingly harmful to companies struggling to maintain hard-earned market share.