I don't think it's primarily a Christian "thing." I mean, I've known plenty of girls who would be more than happy to have a go at Mr. Happy for you as long as you abided by the "rules." There was really only one rule. Take it out, play with, rub it with various parts of the body, give it a lick, but whatever you do, for chrissakes don't stick it in.
I was good friends with a girl, who wasn't particularly religious, but followed this same creed. She had guy after guy visiting her for "favors" and it didn't bother her a bit. At a party one time, I watched her get one fellow off in the corner with her hand and then go visit another fellow in the back for some "quality time." I listened to this same girl at work about a week later extoll the virtues of being a virgin in this day and age.
You can call it what you want you, but the fact is once your 21st digit shows up, it's some form of sex. It doesn't matter much where you
don't stick it.