The German driver had made his opinion clear at a news conference ahead of last weekend's Malaysian Grand Prix when asked about the much quieter units that have replaced the screaming V8s.
Formula One supremo Bernie Ecclestone and Jean Todt, president of the governing FIA, agreed at the Bahrain Grand Prix on Sunday that the sound would be tweaked with the full agreement of teams.
While the FIA has cautioned drivers about keeping their language clean in public in the past, Todt told reporters he respected Vettel's opinion and would be happy to discuss the situation.
Dennis told Sky television that he was disappointed, however.
"Being a world champion requires a dignified approach to everything, so putting aside the language, even the sentiment is inappropriate," said the Briton.
"The simple fact is if he was sat in a Mercedes he would be extremely happy, and I'm quite sure any four or five-letter words would be more of joy.
"He should just reflect on the fact he has had a period of dominance, and just because that dominance is being shaken by Mercedes, doesn't give him the licence to be disrespectful of the obligations placed on him as a world champion."
Mercedes, with Britain's Lewis Hamilton and Germany's Nico Rosberg, have won the first two races of the season from pole position and their engines have been dominant.
Vettel won the last four world championships, and nine races in a row to the end of last year, but Renault-powered Red Bull have been playing catch-up in the new era.
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