When you have an open wound on your hand (in my case, from slipping while trying to drive a screw into cement backerboard and thrusting the full weight of the drill and it's sharp, pointy Philips-head bit into the tip of my index finger), and you are spreading grout on new tile, for the love of God, wear gloves. I would especially advise against using that same finger to smooth the grout line, further driving the grout into the open wound.
I think that finger is now completely devoid of fingerprints. I could commit a really heinous crime, and they'd have no way of catching me. As long as only my index finger touched any surfaces.