The sports implement that must not be mentioned is the title of an email (#0922) from Stefan Rahmstorf to Jonathan Overpeck and the IPCC 4AR paleoclimate chapter authors.
You can't say he hasn't got a sense of humour.
The text is less funny - it's a call for proxy reconstructions to be normalised on the twentieth century values. Otherwise they might diverge. And we can't have any divergence on show I guess.