I have had the pleasure of fucking about 6 men and 15 women up their asses & have been fucked few times so I know the pleasure of anal sex. The asshole is the most sensitive part of the human body and once you know how please a man/woman ass then you can be assured they will back for more... Don not rush it. Show her/him an adult DVD involving anal sex then approach the subject. While having sex doggy style with the woman insert a finger then 2 in the asshole. having them feel the hidden pleasure of ass stimulation, lick her ass also while licking her pussy... Next time use a small dildo or a cucumber stretch the asshole... after she agrees the ass fuck , make sure she is served with alcohol , a lot of foreplay including licking the pussy and the asshole.. then use a double penetration of yr dick in her pussy and a small dildo up her ass... then switch penetrate the asshole with yr dick and the dildo (after cleaning it) in her pussy. Just insert the head of yr dick in her asshole and let her push back on it until she is comfortable with yr size.... let know if work for you...