All right, I'll bite. "Rape culture" is the popular term for a culture that, while perhaps not explicitly endorsing or condoning rape, does enable it. The chief symptom of "rape culture" is a social stigma that makes it difficult for victims to come forward and address their experience, whether that's seeking emotional/medical/psychological support or pursuing legal action.
Calling alleged victims "dumb *******" reinforces this social stigma and so is evidence of a "rape culture".
Men also suffer in a "rape culture", both as actual victims of assault and as the target of social pressures to perform and "get laid", equating their value and success as men to the number of partners they've had. Machismo-run-amuck leads to its own set of emotional and psychological issues.
Now there is an absurd wing of the "anti-rape culture" movement (as there is of every movement) and it's easy to find that absurdity on the internet, but I think the important thing to remember is to be mindful and compassionate when talking about rape, especially when all we know comes from some Tumblr posts and 3rd parties.