“Get the sack” means “to be told to leave your job”. Example: He got the sack when they found out that he’d lied about his qualifications. Origin: This idiom comes from the time when workers carried all their belongings and tools around in a sack.
“Butter someone up” means “to flatter or be nice to someone in order to get something from them”. Example: I’ve stopped answering my phone when Jenny calls me. She always butters me up with lots of compliments and then asks for a big favour.