How would you define an act or a person who answers a question with an answer they know might not necessarily be true, for the sake of providing one?
eg.
Tim – What's the name of Microsoft's new operating system?
Bob – Ermmm. Windows 9.
Tim – Thanks Bob.
Best Answer
If a person with a normal attitude receives a question to which he/she doesn't have an answer to, a reply would be "I have no idea. Why don't you look up the internet?" or "I don't know."
Know-it-all is the word describing;
A person who behaves as if they know everything
from Oxford Advanced Learner's Dictionary.
Someone who thinks he knows everything and refuses to accept advice or information from others.
from Thesaurus
Know-it-all can be used as an adjective.
8 Tips for dealing with a know-it-all coworker.