The words of a person are a reflection of his/her inner self. Cannot fool people too long, once someone has opened his/her mouth (and in some instances the pen or digital input device). Take a tip from Froggie, it always pours out, for good or otherwise.
We find that Yaakov avinu, how hard he tried to fool Yitzchak Avinu by pretending to be Esav, once he opened his mouth, his inner self showed and shined out. He could not help it. No – a real oved HaShem, with refined character cannot get himself to verbalize the commoner’s street “language”.
So