Very slick indeed.
Phrase used to convey:
1)A sense of elegant suavity
2)A smooth, dashing je ne sais quoi
3)Class coming out ones' ass
Impressed Socialite #1:"I say, did you see how William butt-fucked that bunny-rabbit without soiling his cummerbund or spilling his green tea?
Impressed Socialite #2:"Yes, he's as slick as snot on a doorknob."