I have wondered about this, tried it once and thought Meh not again. Now these are just my thoughts what others do does not matter to me but would like to know that the turn on is.
First you are sticking your dick where crap comes out of and only crap. Some people talk about ass to mouth and then DFK There is a far better opening just an inch or 2 away which I prefer. Jim Jeffries the comedian but it best " Men like anal sex because women fuckin hate it ". I know it is just a joke but it is funny. Would like to hear other opinions, from SP's also if possible.