Update: Thanks to some brilliant suggestions from you all, we have an even better contender - A man who ran in the 1998 federal election named 'Prime Minister John Piss the Family Court and Legal Aid' who received a whopping 183 votes for the party 'Abolish Child Support'. Sounds like a lovely guy.
Unfortunately for Mr Prime Minister Piss, this name change came back to haunt him after he was denied a passport a few years later due to the name. This led to this quite incredible entry into Australia's case law that is still frequently cited today:
Unfortunately for Pisso, the court ruled that the government was right to deny him a passport, on the grounds that the phrase "Prime Minister" might be considered by some to be offensive.
Australia went on to change the laws around name changes as a result of Mr PM JP, making him the first and last Prime Minister Piss we'll likely ever see on the ballot in our lifetimes, and democracy is all the poorer for it.