The two small dots above german letters. Usually used to move the syllable sound to the front of the mouth, so 'ooo' becomes 'oh' and so forth. Also associated with making something seem cooler, or more edgy. This process is commonly associated with nouns.
über, köhn. And to make something more intesne - Joseph becomes Jö-sef.
He just thinks he's all that because he has an umlaut in his name.