It matters that it is considered an insult, no matter how derived. And since it is a gross reference to a sex act, it is not polite, despite how it may have come to be.
Therefore, being used as an insult, it is childish. However it was created. When insults rather than content are used in political discussions, the natural assumption is that the insulter has no content. When people use childish insults in adult discussions, they deserve to be called on it. Whatever the history of said insult.
P.S.
Funny how you keep using my AV name when replying to others. On this point somebody else without a login/coward is making supportive statements, but that does not make them me. You can think they are if you wish, but you would be wrong. As you can see, I am perfectly capable of replying with my own login.