I've always thought that at least part of the implication (not necessarily the origin) was that the other person (and perhaps the speaker as well) might be too refined to have learned these words or understand their true import.
Even though what I'm about to say is unintelligible, I'm going to say it anyway.
Here, I'm handing you an excuse so you can pretend not to be embarrassed or feel you need to correct my crude ways.