I don't think Rossi is a dirty rider compared with most, but consider the Gibernau last corner Jerez 2006 pass and particularly the Sepang 2015 take-out to be dirty by any standards.
Perhaps Valentino has a point in logic though, and Jorge should describe him by a more defining term, in which case he should call him either a prima donna or someone who has serially mobilised his fans as a weapon against his rivals.
Lorenzo never called him dirty though not once. He said other riders overtake cleaner which isn't a complete lie. He said his style is to overtake aggressively which again is true.