When Donald Trump used this phrase in a statement against Hillary Clinton, he showed how vulger and disgusting he really is. It is vulger and inappropriate and offensive toward women. Trump used this to degrade Clinton, but he only degraded himself - no one respectful and worthy of running the U.S. would use this term against another candidate.
Obviously, the word "schlonged" is an inappropriate and vulgar word. It is a makeup word meaning the sexual part of the men' organ. If one is using this word to express his or her anger, it is somehow inappropriate especially if he or she is using to scold the others. This, I don't agree with this word.
Schlonged is definitely a vulgar and inappropriate word. It is a slang term and should not be used publicly. I don't know how the word ever got its meaning, but I clearly don't think it should be used. I can't foresee a time when the term schlonged should be used.
As of right now probably not, but who knows in the future. It's always changing and what was once considered vulgar may not be in the future. This also works the other way. It is just what society deems vulgar at the time. As of right now I don't think this is the case with this particular word.