Only way that you'd get raped at an anime convention is if you fit this criteria:
1) You're cute
2) You're showing skin in some way
3) You make adorable sounds like 'Kyah'
4) You're asian or you can speak an asian language somewhat
5) You manage to attract a fleet of fanboys in under 5 minutes.
Lets say hypothetically. What if you get raped by 5 or 6 girls who always wanted or loved Mio but weren't lesbians, then what? Long shot I know, but there has to be some girls out there who do. As I always say "You can't rape the willing."