Sweet'N'Low
False kindness for someone you hate but have to tolerate. Alternatively, false kindness coloured with ulterior motives.
"John is such a brown-noser; he keeps giving the boss Sweet'N'Low."
"Get outta here with that Sweet'N'Low. I know you're just trying to get in my pants!"
"Get outta here with that Sweet'N'Low. I know you're just trying to get in my pants!"