I was with a girl that was real bad at wiping. Every other time in doggy it stunk shit. Once in the act, i got tired of it and told her she needed to take a f-in bath. Put her clothes on right after I said it left didnt answer my calls for over a week 
So girls use fcking WET WIPES or shower Before fucking. Nothing worse than a stinky ass!
Telling ANY girl ; " You're butt smells"; is the end all/be all of insults.
I was with a sexy babe once and she got up on all 4's for doggy style.
Sadly, she has a small but obvious "skid mark" on her upper right butt cheek close to the crack.

What to do? Her butt cheeks were quite pert , but the mark of shit was there.
I needed to deal with this but I needed to be careful to avoid pissing her off.
I had to distract her in a sexual way.
Sooooo ,I licked my fingers, fingered her with the left hand .
Then I quickly wiped away the skid mark with my right.
Once the way was clear, I mounted her and went to work.