Comments like that are just stupid and disrespectful to rape victims. Yes, you would mind being RAPED by a girl, because rape is a forceful, violent, unwanted sexual act.
It can happen man-on-woman, man-on-man, woman-on-man, or woman-on-woman. Regardless of the biological responses, it is rape if there is no consent. An erection =/= consent. As a man, you should know that erections can happen for a number of reasons. Besides which, many women who are raped experience vaginal lubrication and even orgasms. Your body betrays you sometimes. It does not mean you were willing and it's a factor that many rape victims feel extreme guilt and disgust over, thinking they wanted it.