ON THE bus home from university one day, I met a former high school classmate who spent most of the 40-minute journey being rude to me.

He was always a smug know-it-all who loved the sound of his own voice but the casual cruelty of what he was saying to me in such a public space took my breath away.

Increasingly mortified as he went through everything he thought was wrong with me, including (crucially, probably) my rejection of him, I sat silently, feeling slightly sick, until it was my stop and I could escape.

It was horrible, and it was hurtful – as you can tell, from the fact I still recall it today, many years later – but after I rushed off that bus it was over.

None of my fellow passengers felt the need to wade in, or to send him a smiley-faced thumbs-up from across the aisle.

READ MORE: Ann Fotheringham: Is tea the answer to life's problems?

I did not go home to discover his skewed, unpleasant version of me was all everyone was talking about, nor did I have to defend myself endlessly to complete strangers outraged on my attacker’s behalf despite not knowing him, or me, or any of the background.

In a recent article in Psychology Today, psychologist and mental health writer Mariana Plata says rudeness is ‘like a neurotoxin, a poisonous substance that negatively affects our nervous system...it affects the way we think, act, and feel.’

People are unbelievably cruel to others when they can hide behind anonymity.

Carelessly insulting someone, whether you know them or not, has become commonplace.

There is always someone with an opinion who is desperate to spit it out there, determined to get the last word, regardless of how much or how little knowledge backs it up, uncaring about how it might impact upon the subject’s wellbeing.

Ironically, I was reading a newspaper interview with First Minister Nicola Sturgeon and feeling shocked by the truly vile, personal insults posted about her when I heard TV presenter Caroline Flack had taken her own life.

Whatever drove her to this, the barrage of online abuse she received in the months leading up to her death was shameful.

READ MORE: Ann Fotheringham: Why bother with Bond? Let's tell our own stories.

American essayist Ralph Waldo Emerson said: “You cannot do a kindness too soon, for you never know how soon it will be too late.”

We should all take heed, because this epidemic we are facing, this rush of rudeness, is truly toxic.