In Mail, go to Preferences > Rules and add a rule which says 'If From' contains 'person I really hate' perform the following actions 'Delete mail'.
(It might be best to move it to a folder you create for the purpose rather than delete it, at first anyway, just to check you've got the syntax right and its doing what you intend - voice of bitter experience speaking, having just nearly lost all my inbox..........)
no, its for a mate of mine who is within a large company and is getting dodgy mail from someone who is bonkers, but the sender is sending it to the sales@whatever and the company just forward it internally to mymate@whatever causing maximum embarrasment