Lubriciously is how someone looks, speaks or acts when they show sexual interest in that oily, unpleasant way. “He grinned lubriciously” means the grin was lewd, not friendly. It has the same formal, written flavour as lubricious — you are more likely to read it than hear it. Though actually, the -ly here does not mean “in a slippery, well-oiled way”, which is the trap the spelling sets. This adverb stays with the sexual, critic’s sense. Built in the ordinary English way: adjective plus -ly.