The Official TWiT Wiki:Block policy
Every user on the wiki has fair and equal rights to edit and parpicipate in this community. There are some who may disagree with a certain policy, questionable content or some who just wants to mess around for personal amusement. This is where blocking a user comes in, blocking is a way for sysops to prevent the user from editing the wiki (though they can still view the content). Blocking a user is a powerful thing and should be used responsibly and fairly, always use good judgement when blocking a user.
Vandalism and Spamming
Vandalism and Spamming has been a tough spot for blocking because you can't determine whether they're disagree with something or doing it just for personal amusement. This is where your personal judgement comes in, as not every person is the same and they have different reasons for what they've done. What you could do first is leave a message on their talk page as a warning, talk it out if you can and try to resolve the situation. If he repeats whatever vandalism or spam he was doing then you'll want to leave a warning block, increasing for every repeat offense (that's every time he/she does it.) until it reaches infinite or you decide that he is incapable of learning his leason. Additionally, the user may see the error his way and may reform himself to become a proper member of the community. Again, use extreme judgement when dealing with situations like this.
Inappropriate usernames that contain explitives, slang terms for sex, ASCII art about inappropriate items or anything that's considered offensive and tasteless may be blocked, make sure to check that the autoblock is off so that the user can register a different, appropriate username.
Random people or users may have a grude against a user or another person and as such, calls for resolution conflict. Users will likely leave a nasty message on the user's talk page, vandalize a userpage with something nasty, or vandalize a random page with a nasty comment to that user when personally attcking someone. These attacks can mostly be resolved by talking with both users directly and working out their problems one by one, which usually works. If the user keeps attacking the other user then you may give him a cooldown block to let him calm down. Suggestively if he doesn't cool down by the time the cooldown block ends then use your judgement to think of an appropriate block, while trying to resolve the situation. Stay persistent when resolving these situation and you'll make it through the end.
Unblocking or shortening a user happens when the blocking administrator decides that the block should be reversed, when the circumstances change or when there has been a mistake of some kind. Unblocking can also happen when a user appeals the block or requests unblocking, princably using the (Special:EmailUser) function. When a user requests unblock, an administrator may review the block log, their edits, and additional information provided by the user, to determine if the user should be unblocked, or not.