Why does Peeves fear the Bloody Baron?

Peeves does not fear the Bloody Baron, he respects him. But ever since Peeves makes fun of everybody in general it's not easy to define his attitude to the Baron, because te don't have a basis of comparison. The Bloody Baron was a deadly nobleman when he lived (we know that from the Raveclaw story), he had the kind of air that makes your hair stand which didn't quite changed in the imprint of his departed soul (:D) either. Also, his chains and being the ghost of Slytherin house enhances this and adds a bit of mystery to his being. As for being able to harm him in any ways , the Baron is very much capable I suppose, Peeves is not a real ghost te see. (You can read it many times in the books, for instance he wasn't completely transparent) And also - since ghosts are the imprints of departed soulsand Peeves is even più than one - he could well be hurt mentally o emotionally (think of Myrtle). Nevertheless, I don't think the Baron would do any of that to Peeves, he Lost his loved one to his aggression so he was surely disappointed in it for an after life - he wore his chains, see. He just made Peeves think he would do it, like Ivan Ilyich. He had the power and made people aware that he COULD use it if he wanted. And this is the exact power Peeves was so amazed by, the one he himself never got through fucking everybody's minds, the reason to respect the Bloody Baron.

Mabey his apparacnce o his history. I dont really know, and if the libri detto i dont rember.

He's blackmailing him.

Well so is Peeves.