Edmund Grubb was fat and did not have the endearing traits the Fat Friar was blessed with, he was simply annoying. Despite this, it seemed Dumbledore never grew exasperated with him. He was a victorian ghost that had a seriously haughty attitude, he was also still very bitter with his expiration. To soothe his bitterness, he kept everyone from entering the dining hall, especially right before the sorting. He often had a smug look as he threatened anyone to move him.
More often than not, he would leave within perhaps the next minutes but today he stayed smug as he stayed even longer. Not even any of the other ghosts could move him so when this happened they all played along, waiting and perhaps taking time to introduce the children to teachers. He was causing a massive hold-up and negativity throughout the hall. He finally decided to leave and all was right for now as he now floated along through the hall instead.
He could feel the piercing stares in his back, but he didn't care. He was a petty fat man, so it didn't matter, as long as he got the upper hand.
He enjoyed the attention, even if it were negative, everytime he blocked the entrance accompanied by groans.