Last week, a photo of my head appeared above a story on an American news website, for reasons too convoluted to go into right now. It wasn't a particularly good picture of me – they rarely are, as you'll see by glancing upwards to the top of this column – but in the comments section people had begun openly to mock my stern expression and balding head; one suggested that I looked like a potential menace to women.

Slightly upset by this, I emailed the person who wrote the story, pointing out that this was a little unkind. I was probably hoping she'd have the offending comments removed, but she just sent me a sympathetic reply, saying how terrible it was that someone should say such a thing. Free speech, of course, is more sacrosanct than my feelings. And if someone thinks that I look like a rapist and wants to tell the world, there's not a great deal I can do about it.

But what if that became a sustained campaign of public badmouthing? Is there a point at which legal systems will say that enough is enough, and stand up for the individual on the receiving end? Well, that question is being considered by a federal court in Maryland; William Lawrence Cassidy stands accused of posting some 8,000 messages on Twitter under various pseudonyms, venting his fury against one individual, a Buddhist leader by the name of Alyce Zeoli. ("Do the world a favor and go kill yourself. P.S. Have a nice day" gives you a flavour of Cassidy's general tone.)

But while Zeoli claims to have lived in fear of her life during this campaign, the fact that it was allegedly waged on a public forum seemed to offer Cassidy protection under the First Amendment's commitment to preserving free speech. Was he saying something about Zeoli, or was he saying it to her? Was he using the online equivalent of a telephone, or a megaphone?

The answer is, of course, something in between. The legal profession has wrestled with this problem before, and failed to come to a satisfactory conclusion. Paul Chambers, famed for posting a tweet which jokily threatened to blow Robin Hood airport "sky-high" when his flight faced disruption, was found guilty of sending a "public electronic message" that was menacing in character. But was it public? It could be seen by the public if the public were looking for it, but it was really intended only for the community who regularly read his tweets. And as the Communications Act 2003 doesn't recognise the concept of "semi-public", Chambers was convicted; his High Court appeal will be heard later this year.

Meanwhile, in the US, campaigning group the Electronic Frontier Foundation (EFF) has expressed similar disquiet about the inability of US law to deal properly with the Cassidy case. At the moment, he is in jail awaiting trial for violating legislation drawn up to deal with stalking, but he wasn't doing that; he was, apparently, mouthing off relentlessly.

According to the EFF, this sets a dangerous precedent – namely that "the use of a public communication service like Twitter to criticise [an individual] can result in criminal liability based on the personal sensibilities of the person being criticised".

This will continue to be a problem for as long as human beings continue to be furious with each other – and on the internet, such anger is endemic. Zeoli's Buddhist website advises that "love, forgiveness and acceptance are the way of peace and enlightenment"; it's a beautiful sentiment, but sadly not one that's observed much online. With no laws to protect our feelings, it's down to us to toughen up.