"A physician we interviewed recounts the story of a laborer in Africa who worked around vats of sulfuric acid -- one of the most caustic forms of acid. The man fell in one day. He quickly leapt out, but was covered in sulfuric acid, which immediately began to burn him chemically. In a panic and excruciating pain, the man ran outside. By the time his coworkers caught up to him, the man had essentially dissolved.
The acid burned the man to death, searing through skin, cauterizing blood vessels, and eating through organs until he died. The pain would be unbearable, and the circumstances irreversible. This is unquestionably a really bad way to die."
-as taken from howstuffworks.com