Technically you are not allowed to provide fake information, although you may use an identity proxy as long as they provide the means to contact you in case of a dispute. In reality, enforcement of valid identity information is essentially non-existent.
I'm personally aware of at least one incident in which someone who had their domain revoked for 'joke' contact details in the whois db. Then again, istr they did piss off
an old-school sysadmin (in the a.s.r sense).