Consider carefully before sending angry e-mails to someone. One paragraph of venting often leads to pages more of time-wasting payback.

At least, that seems to be the motif behind David Thorne’s “The Internet is a Playground: Irreverent Correspondences of an Evil Online Genius,” which documents the struggles between one bored Australian graphic designer and his host of unfortunate correspondents. The nonchalant tone in this collection of tongue-in-cheek e-mail exchanges proves that people will not only hang themselves if you give them enough rope, but leave enough for you to jump rope with.

Much of the hilarity in Thorne’s deadpan sarcasm comes from his ability to be both unfailingly polite and unconcernedly crass. His approach to those who have trespassed against him — or even those who have legitimately asked to be paid for services rendered — is more about turning polite agreement into insult than turning the other cheek.

Landlord thinks your premises isn’t clean enough? Send him your sincerest apologies and a drawing depicting him being eaten by a shark.

Cops think you shouldn’t joke about selling drugs on your web site? Tell them how much you respect them by describing how you once failed a police exam because you were intelligent enough to show up on time.

Some of Thorne’s exchanges begin with the whimsical and end in the absurdly offensive.

Coworkers hoping to take advantage of Thorne’s graphic design skills for lost-pet flyers receive overwrought descriptions of their injured and dying animal on the side of the freeway for their trouble. And teachers who take away his son’s campus computer rights are encouraged to use disciplinary actions such as caning and starvation if they don’t find the current punishment to be harsh enough.

But child and animal rights advocates shouldn’t be concerned. Thorne’s more extreme writings are funny because their absurdity is to be taken with a grain of salt — or perhaps a carton. More than likely, if the e-mails were exchanged as Thorne claims, then their outlandish nature was exactly what allowed him to keep his job and to stay out of jail — other than an admitted arrest for unpaid parking tickets.

Regardless of whether the e-mails were constructed or actually exchanged, Thorne’s acidic tongue and his varied use of rude and heartless graphic art will cause some to wonder if they too can avoid late fees and excessive bills with the clever use of handmade clip art.

And those who find the book humorless would do best to keep their critiques to themselves — or at least, away from Thorne’s inbox.