When another man rubs your shoulders and/or back in a homosexual manner, one is being rubbed like Rapps would rub. It could also describe a homosexual/heterosexual hand job.
However, it can also be used to describe a back and/or neckrub in a homosexual/heterosexual/platonic situation.
"Honey you are not getting the knots out of my back. Rub it like Rapps."