A german phrase, well known by the Streamer "MontanaBlack88".
It's used in a conversation as a random reply when someone is about to show off something they are proud of.
It could also express your indifference of someones question or statement in a ironic way.
Race: "When yer famous, the woild is yer erster."
Newsies: "Your what?"
Race: "YER ERSTER. Hey yk yer fancy clam wit the poyle inside!"
Newsies: "OYSTER"