Other forms: buttering up; buttered up; butters up
Use the phrase butter up to describe someone going overboard praising or complimenting another person — especially in an attempt to get something in return.
You might try to butter up your math teacher in order to get a better grade. Flattery is unlikely to work, though, unless you're also really good at algebra. When you picture spreading too much oily butter on a piece of toast, you get a sense of what it means to butter someone up.