New Zealand Prime Minister John Key was recently asked to provide "any evidence to disprove the theory that [he] is in fact a David Icke style shapeshifting reptilian alien ushering humanity towards enslavement." Key, in a congenial manner atypical of shapeshifting reptilian aliens, responded.
To the best of my knowledge, no. I've taken the unusual step of not only seeing a doctor but a vet, and both have confirmed I'm not a reptile … I've never been in a spaceship, never been in outer space, and my tongue's not overly long either.
Auckland resident Shane Warbrooke, who first posed the question via an Official Information Act (OIA) request, said he was happy with (but unsurprised by) the president's response. He did complain, however, that the government "waited the full 20 working days they are allowed before getting back to me."
The White House responded to a similar accusation in March of last year. (Notably, the White House didn't go so far as to deny anything.)