Robert Riley, 42, was last week sentenced to eight weeks in jail for posting offensive tweets about Leeds teacher Ann Maguire, who was stabbed to death.
1. Don't people tweet offensive things all the time? Why do only some people get convicted?
This is a very good question. Basically, you can't say anything – in an electronic form or otherwise – that is "grossly offensive or of an indecent, obscene or menacing character", according to the Communications Act 2003.
That doesn't mean you can't say anything nasty. Grossly offensive means something that is likely to shock most people, like gloating about the murder of a much loved and respected teacher.
Context is everything: an Appeal Court judge in 2006 said that the "same content may be menacing or grossly offensive in one message and innocuous in another". For example, quoting offensive dialogue from a film is different to using the same words to annoy someone.
2. Does someone have to complain to the police for someone to be arrested for tweeting?
No. Crown Prosecution Services guidelines for prosecutors, issued in 2013, are clear that "there is no requirement that any person sees the message or is offended by it".
3. If someone is only a minor, isn't that a defence?
Nope. A 17-year-old was arrested for sending offensive tweets to Olympic diver Tom Daley in 2012. People aged 10 to 17 are usualy dealt with by youth courts and given different sentences but there's nothing to exempt them from this legal threat.
4. What if I was really, really drunk?
Judges and magistrates don't tend to like that line of defence very much.
Isabella Soley, one of the two people convicted of sending abusive messages to feminist campaigner Caroline Criado-Perez admitted she was "highly drunk" when sending them, as was Michaela Turner, who received a suspended sentence for Facebook messages about murdered solider Lee Rigby.
5. If I defame someone who can't afford to sue me, is that risk-free?
Ah, no. So then there's the risk of defamation and social media. Anything you say that is "likely to cause serious harm" to someone or "expose them to hatred or ridicule" could potentially see you appear at the High Court, or more likely see you make a grovelling apology. This applies whether it's Facebook, Twitter, in print, or you wrote it on a wall somewhere.
The best defence is that the allegation is true, and in the context of "slagging someone off", it's going to be hard to convince a court that someone definitively is a "bellend". Plus, defending yourself in court is a very costly business.
You could say there's more chance that a rich, famous person will have the resources to sue, but there are "no win, no fee" conditional free arrangements these days that mean that ordinary Joes can start libel proceedings.
6. So does the law essentially say, "Don't have any fun on Twitter" ?
The CPS's guidelines say prosecutors should "have regard to the fact that the context in which interactive social media dialogue takes place is quite different to the context in which other communications take place".
It goes on: "Access is ubiquitous and instantaneous. Banter, jokes and offensive comments are commonplace and often spontaneous. Communications intended for a few may reach millions."
So "banter" is fine – for a prosecution to go forward, it can't just be: "Offensive, shocking, or disturbing; satirical, iconoclastic or rude; an unpopular or unfashionable opinion ... even if painful to those subject to it". For it to be malicious it has to go beyond those definitions.
7. Which subjects should I avoid?
The law doesn't clarify any specific subjects that any more dangerous to tweet about than any others – but there's a clear trend towards convicting people who say disgusting things about high-profile people and news events, such as the Ann Maguire killing and the murder of the solider, Lee Rigby.
The increased interest around a news event like that certainly helps amplify someone's vile tweets – newspapers love a "troll Twitterstorm" story – thus meaning that people tweeting offensive things about normal, everyday people not involved in anything extrordinary.
Twitter says it has a clear process to work with the police on this.
8. But hang on, my tweets aren't the same as the front page of a newspaper, are they?
You may have a point, but that's not how the law sees it.
Media law expert and journalist David Banks, co-author of MacNae's Essential Law for Journalists tells BuzzFeed: "It's considered a form of publishing, but it's not the same as the front page of the Daily Mail. Newspaper editors have done far more to jeapordise the legal process and the last time any of them were jailed was in 1948," he says.
"It's a major issue for the lawmakers and also the platform providers, in terms of what guidance they are giving people. It's not in their interests to create a platform that can get people criminalised.
"It does seem that social media is providing a constant challenge to the way the law operates in this country.
"The conflict is that the social media is conversational in its nature – it's a social medium and people get used to its banter-laden expressions of opinions. It's the saloon, but it's all on the internet.
"But the point is that when people said something in the saloon it wasn't a problem. On Twitter they are having the same conversations, but they are are being repeated and retweeted and can be seen by anyone. That's the real challenge and it's one that the government is ducking."
9. What if I just retweet or repost something someone else said?
That's no defence either. The CPS, in its guidelines for prosecutors, makes clear that retweeting and repeating something should be treated in same way as the original post.
10. Isn't there a free speech law protecting us all anyway?
Yes and no. There's no specific free speech law in the UK, but we are covered by the Article 10 of the European Convention on Human Rights, which guarantees the right to freedom of expression.
Much of media law is concerned with finding the balance between Article 10 and other legislation governing what we can and can't say, including defamation laws and the Communications Act, and every case is slightly different.
Article 10 makes clear that each European country will have laws that to some degree curtail freedom of expression in some way, "the protection of the reputation and rights of others". In short, you have no right to expose someone to substantial hatred and ridicule or anything that's grossly offensive.
11. If I have broken the law, is it OK if I just say "sorry"?
It can certainly help you.
In deciding whether something is malicious, prosecutors are told to decide whether the poster has shown "genuine remorse" and if they've taken swift steps to remove or block the post from public view.
This can also have a big effect on the kinds of damages that would be paid out in the event of an unsuccessful libel case.