What's with the stupid joke about another woman leader, Hillary?

There's been a lot of media sniggering in New Zealand, as well as the US, about Hillary Clinton's gaffe in referring to Helen Clark as the "former Prime Minister of New Zealand" when she's still in office. But we're used to Americans who have no idea where NZ is, let alone who the PM is. What I found far more offensive was the unlovely sight of one would-be woman leader deciding to tell a stupid sexist joke about another woman, who happens to be one of the most successful Western women politicians in history (Labour Party leader since 1993, Prime Minister since 1999). Clark, along with her women ministers, has been the target of strongly gendered attacks for years. In the 2005 election campaign, for example, National Party supporters tried to drown her out during a debate with calls of "no-kids lesbo" (needless to say, these were edited out of the TV broadcasts). But it was a shock to see Hillary letting rip with such a nasty little put-down.