Forest's recent improved league form was blown apart by Yeovil who went into half-time two goals to the good.
"I'm struggling to find the words to describe what I've just seen - it was disgusting," said Megson who also saw Gareth Taylor sent off.
"There was arrogance, a lack of work, lack of quality and there's no excuse for it. A few home truths have just been spelt out for the players.
"If I had known that was how we were going to play, I would have told people not to bother coming to support us."