I've done it a lot and it usually flounders the heck out of them and they drop it real fast. There are people that harass just to get others upset or hurt so when you're super saccharine back, they don't know what to do about it. Heck some of them stick around and change their tune
I believe you should always forgive them, and yes, 'kill them with kindness'.
Hating back on them is just making you a worse person and it doesn't feel good to always hate on someone. Its upsetting to have someone hate you for possibly no reason but you should try to talk about it with them or try to understand their position and on top of all of it forgive them.
I mean, if someone spouts hate at you, they're probably going through something horrible in their lives, and you just happened to be their outlet. I believe in this saying, but I just don't think I have the attitude to pull it off ;___; I really wish I do