[Fhios]

Google it or something: Greasers were a working class youth subculture that originated in the 1950s among teenagers in the United States. Rock and roll music, especially rockabilly, was a major part of the culture, and styles were influenced by singers like Elvis Presley, Eddie Cochran, Gene Vincent, Johnny Burnette, Vince Taylor and Ritchie Valens, but the two main figures of the look were Marlon Brando and James Dean.

But no. That's not what I meant. I meant just in general slippery like a lawyer in a sharkskin suit.

[Smokin' Joe]

Then why don't you use "polished" or "slick" and avoid:

"3. Offensive Slang Used as a disparaging term for a person of Latin, especially Latin American or Italian, descent"

(From TheFreeDictionary.com)

Many terms have multiple meanings, and using "greased" is an odd usage for describing a verbal presentation--one I have not seen used before. It reeks of being a cheap pejorative, and I think we can do better here.