I'm writing a character who is cynical and cruel, but the way he speaks is very sarcastically sweet to further emphasize how jaded he is by the nature of the world and men, but I can't find a word that describes this type of "fake sweetness". He very often says stuff like "My my, if you're so bothered by my antics, what are you going to do about it?" and just sounds so pleasant and well-versed, but his tone is dripping with sarcasm, but sarcasm has connotations of bitterness or scorn and he's not being scornful, he's genuinely curious what they come up with in the hopes of entertaining him.
I'd go with saccharine
too sweet or sentimental : sweet or sentimental in a way that does not seem sincere or genuine
This derives from early use of saccharine, which was one of the first artificial sweeteners. While the resulting taste was sweet, it also had an overtone which made it fairly easy to realize that it wasn't really sugar.
The closest single word may be "gibe". It is the translation of the Spanish, "puya" which literally means "tack" or "thorn," but which is also used to describe a carefully crafted comment that appears to be a compliment, but is actually meant to be deflating to the one for whom it is intended (the effect of a carefully-placed tack).
For example" "That new top is perfect for you. It's remarkable the way it seems to cover those extra pounds."
"Congratulations on the new job! will you be moving out of you parents house soon?"