We went out for lunch this Sunday, so the cap stayed on the drink until Monday. This is something that has happened before, there's nothing unusual about it. However, it's the first time it's happened when my wife has been drinking Tango Mango (or maybe it's Mango Tango). Here's what greeted us on Monday morning:
It looks as if the seal from the cap was very good, preventing gases from getting in or out. The gas in the can seems to have been reabsorbed into the Tango, such that it created a lower-than-atmospheric pressure inside the can. This resulting in a compressing effect from the outside, leaving us with a strange, hexagonal can.
The Tango was still pretty well flat when my wife drank it, though.