P.P.S. I'd like to quote Wikipedia blocking policy, as per the Blocking Policy page:

 Explanation of blocks 
Blocking is a serious matter. The community expects that blocks will be made with good reasons only, based upon reviewable evidence and reasonable judgment, and that all factors that support a block are subject to independent peer review if requested. 

 Notifying the blocked user 
Administrators must supply a clear and specific block reason which indicates why a user was blocked. Block reasons should avoid the use of jargon as much as possible so that blocked users may better understand them. Administrators should also notify users when blocking them by leaving a message on their user talk page unless they have a good reason not to. It is often easier to explain the reason for a block at the time than it is to explain a block well after the fact.

When implementing a block, a number of pro forma block reasons are available in a drop-down menu; other or additional reasons can also be added. Users can be notified of blocks and block reasons using a number of convenient template messages—see Category:User block templates and Wikipedia:Template messages/User talk namespace.