Definition:
: likely to respond to a suggestion by doing or believing the contrary
Example:
"Small boys are noted for doing just the contrary of what they are told to do. Some people who are full grown have the same reputation. These people are called contra-suggestible." — The Trained Nurse and Hospital Review, 1922
About the Word:
Contrasuggestible looks like a fancy word for describing that an adult is acting like a child, and as the citation above indicates, that is pretty much how it is (albeit infrequently) employed. It was first used in the early 20th century, primarily in psychological literature, and doubtless has been of great utility to many psychologists who were finally able to stop barking at their patients 'stop acting like a child!'
