Diet Coke & Mentos:The crazy Freshmaker!

Wikipedia explanation:
(...)The reaction was the subject of an August 9, 2006 episode of MythBusters, a television program on the Discovery Channel[2]. They concluded that the caffeine, potassium benzoate, aspartame, and CO2 gas contained in the Diet Coke and the gelatin and gum arabic ingredients of the Mentos all contribute to the geyser effect[3]. In addition, the MythBusters theorized that the physical structure of the Mentos is the most significant cause of the eruption. When flavored Mentos with a smooth waxy coating were tested in carbonated water, no reaction occurred, whereas standard Mentos added to carbonated water formed a small geyser, by their claim, affirming the nucleation-site theory. Of course a wax coating would render just about anything inert in this experiment; wax-coated sodium would have given the same reaction. This was further supported when rock salt was used as an effective substitute for Mentos[3]. The experiment was also repeated in an episode from Numb3rs[4

URBAN LEGENDS:
In November, 2006, the Urban Legends Reference Pages examined the rumors of people dying from eating Mentos and drinking cola. Their research found that while eating Mentos and drinking cola can result in people regurgitating the foamy result (as evidenced by numerous online videos), no actual news accounts exist of anyone dying from it. However, eating Mentos and drinking Diet Cola in a short timeframe is not an advisable course of action.[5] This theory has also been tested on the Discovery series Mythbusters. They used a human analogue consisting of a pig's stomach with tubing that allowed for the insertion of the Coke and Mentos. The resulting expansion, however was not enough to rupture the stomach. Also, on the episode where they found out what causes the eruption, Jamie drank the mixture and ended up spitting out.[3]