Not using a condom.
The sex was consensual
http://liberalconspiracy.org/2010/12/02/no-wikileakss-julian-assange-isnt-accused-of-rape/http://www.crikey.com.au/2010/12/02/when-it-comes-to-assange-r-pe-case-the-swedes-are-making-it-up-as-they-go-along/Assange is being prosecuted for having sex without a condom, with someone who didn’t mind the lack of condom at the time, but who subsequently was cross about the fact that he didn’t use a condom. Who was a 30something university lecturer (not that it would have made any difference had she been an 18-year-old student).
Swedish law on this sort of thing is, actually so deranged that nobody in Angloland could comprehend it (except for people who’ve read Steig Larssen’s books, at which point various plotlines start making more sense: yes, that whole thing about Salander being held as a ward of the state for no discernible reason, which would have be overturned in a second in any Anglophone jurisdiction, was based on reality. Larssen’s early death? Well, I wouldn’t put money on natural causes…).
So why do the non-Swedish press keep lying he’s accused of rape, rather than something which isn’t a crime (and so which isn’t extraditable) outside of Sweden?
Well, that’d be the “Wikileaks being an massive embarrassment to polite political society” thing. Mr Assange is a threat to the comfy order of international lying, various mad Americans want him dead, and so complying with international pressure to lie that poor bedroom etiquette is the same thing as rape fits in.