I used to work with a bloke who was bright, witty and engaging. He was fun to work with and was always ready with a sharp retort.

But he did have a peculiar take on life.

He just didn’t see things the way most other people did.

If something happened in the office, if the company was making changes, we would laugh and joke about it and come up with the most fanciful, unlikely scenarios about why the bosses had decided to take a particular course of action.

The same would happen about stories we were covering.

There was always a little ‘graveyard humour’ flying about.

For the rest of us, that would be the end of the matter.

We’d had our bit of banter and moved on with our lives.

But not this particular colleague.

Something strange would happen.

He would go home for the evening and by the time he got back into work the following day, all those fanciful, unlikely scenarios had somehow crystallised in his brain and now, as far as he was concerned, they were incontrovertible facts.

And there was nothing we could say or do to persuade him otherwise.

He was right (in his mind in any event) and that fanciful explanation was now the only reasonable, logical explanation, even if the evidence pointed elsewhere.

Thankfully, this was back before the advent of social media.

The only recipients of his sometimes wild conspiracy theories were us, his colleagues, and maybe his mates down the pub.

I can’t help but wonder just how much trouble he would have found himself in if Facebook and Twitter had been invented then.

Which leads me on to the point of this column.

Not for the first time I feel it is my public duty to warn people that they are legally responsible for everything they post on social media or on-line forums.

The protections that are afforded by freedom of speech only go so far. And don’t think that posting under an alias will make you impossible to track down either.

And I’m sure those posters truly believe what they are writing.

At various times, either on Facebook or on the comments section of the Guardian’s website, I have been called an arch Tory, a Labour-leaning shill, and someone who hates Warrington.

None of those things is true but I don’t have the time, energy or inclination to engage with people who have already made up their minds.

Of course, we have seen a recent example of a former Labour councillor – using an alias – being convicted under harassment legislation after posting comments about former Warrington North MP Helen Jones.

The councillor’s defence said the comments were simply ‘freedom of speech’ and ‘legitimate criticisms’ and was not aware that Helen Jones was aggrieved by them until police informed him.

And there we have it. One man’s ‘freedom of speech’ and ‘legitimate criticisms’ were enough to land him in front of a district judge.

As a regular observer of the curious world of Facebook groups and comments posted on news websites in the town, I truly believe there are one or two other public figures who, if they were so minded, could successfully take legal action over some of the things written about them.

I wonder what it will take before our on-line trolls realise just how close to the wind they are sailing.