Katy Perry is vehemently denying allegations she sexually assaulted actress Ruby Rose back in the day. Katy's rep tells TMZ ... "The allegations being circulated on social media by Ruby Rose about Katy Perry are not only categorically false, they are dangerous reckless lies. Ms. Rose has a well-documented history of making serious public allegations on social media against various individuals, claims that have repeatedly been denied by those named." The "Dark Horse" singer's response comes just