Is it possible? Can the stomach acids fully dissolve the fabric and other materials possibly found in a hat and can human teeth with average bite force chew through the thicker brims?

Well...stomach acid is quite strong. Put it like this: spilling Coke or other soft drinks (which often have a pH of 2-3) on a bike won't do anything. However, vomiting on it will result in the paintwork being eaten up by the acid in your stomach.
(Thankfully, this hasn't happened to me yet! I read about it in NewScientist's The Last Word column)

quote:

Originally posted by h_gusoff:
Is it possible? Can the stomach acids fully dissolve the fabric and other materials possibly found in a hat and can human teeth with average bite force chew through the thicker brims?

People has even eaten moderate amounts of metal without ill effects... Just read about Mr. Mange Tout for such an example..

Michel Lotito

However, it should be noted that Michel was a very special case, which probably won't pop up again for a long time