"Yeah Dan" is used to insult a Dan. It is pronounced with a obnoxious and slurred voice. Said to a Dan whenever he stuffs up or makes an error. A more formal way to pronounce Yeah Dan is "Yes Daniel".
Yeah Dan means congratulations to a Dan for stuffing up.
Dan says "How was cricket?"
Person 1 replies "I didn't do cricket i did swimming"
Person 2 Exclaims "YEAAAAAAAAH DAAAAAN!"