We cannot have an objective and complete definition of rape which eliminates the perspective of the victim.
Katie Roiphe and many others who claim to want an objective definition of rape falsely dismiss the experience of most rape victims. Their desired rigorous definition of rape in fact seeks to deny many rapes rather than illuminating them.
In the case of someone brushing against another person there are 2 issues: freely given consent and sexualized contact. If the contact is sexualized then freely given consent is a requirement for the sexual contact to be legal.
Many of those who focus on objectivity seek to dismiss certain behaviors at a mechanical level unless those physical movements are always a crime.
For example, an interaction begins with one person holding a gun. Mechanical shorthand: Gun to head, penis in vagina. Rape is clear without asking the person with the gun to her head whether she consented.
This level of objectivity (which turns the victim into nothing more than an object) clearly eliminates most rapes because in most rapes it isn't the stripped down mechanical movement which defines a rape as a real rape. It is the absence of freely given consent.
This mechanical shorthand for rape committed on a date would be: date followed by penis in vagina. Since on a purely mechanical level that is not clearly rape, Roiphe and others dismiss rapes committed under these circumstances as bad sex.
This mechanical shorthand would also eliminate many non-sex crimes, but those who use this shorthand when it comes to sex crimes don't want this standard applied to all crimes. Many burglaries could be reduced to: Person walks through unlocked doorway, carries items out of house. From that "objective" description it would be impossible to know if a crime had been committed.