Can some help me explain this?

I need help explaining to a co worker that fingering is a sin. How would I do this?

It is sexual activity outside of marriage. It is also masturbation. First discussion pre-marital sexual intercourse and masturbation with them, then move on to this more specific act.

DISCLAIMER: The views and opinions expressed in these forums do not necessarily reflect those of Catholic Answers. For official apologetics resources please visit