WHEN does a casual hobby become an overzealous obsession? For me, it happened on an otherwise unremarkable Friday evening when I decided to go for a post-work run. I left the house as a relatively well-adjusted human and returned 40 minutes later having morphed into something else entirely.

I had officially become a running silly billy (the original pitch for this column was “how I became a running w*****” but my editor sensibly decided that we should tone it down a tad, what with this being a respectable family newspaper).

So, how does one become a running silly billy? It takes hold by stealth. A bit like the brain-eating parasites in zombie films, except in this case, rather than devouring human flesh, you have a thirst for expensive trainers and an inexplicable compulsion to wear increasingly shorter short shorts.

To be fair, the signs of my descent into the dark realms of running silly billy had been there for a while. The ever-expanding wardrobe of fitness apparel; obsessing over the long-range weather forecast; rivalling the monkeys at Edinburgh Zoo for number of bananas consumed on a weekly basis.

Yet, on this particular Friday evening, things cranked up a notch. After finishing my run and getting a new personal best (PB) over 5km (3.1 miles), I excitedly sat down to analyse how I had done on Strava, a social networking app used for tracking physical exercise.

Read more: Climbing mountains is overrated – get yourself to the woods instead

Unfortunately, somehow, I managed to accidentally delete the run (clumsy thumbs). My ensuing howl of anguish echoed around the world. When I eventually managed to upload it again, I was convinced the PB had changed to a slower time (yep, I am fully aware of how painfully deluded that sounds).

I messaged a friend – a fellow runner – to tell her about this calamity, pondering how to rectify it. “Oh, I know what’s happened here,” she said. I read on, expecting some pearls of wisdom to be imparted. “You’ve become a running silly billy …” (except she was a little blunter than that).

I burst out laughing because that’s exactly what I was. A running silly billy who, instead of celebrating a new PB, was poring over the data and grumbling about alleged missing seconds like I had lost out on Olympic gold, rather than having plodded in a slow loop around my neighbourhood.

What are the other signs that you have become a running silly billy? Well, your conversational skills take a nosedive, seeing long-suffering friends and family subjected to a never-ending slew of dull anecdotes about your latest athletic endeavours.

Remember the police station scene in Derry Girls where Uncle Colm bores Liam Neeson’s chief constable character into submission? It is like that except with myriad tales about hamstring niggles, missing toenails and hasty toilet breaks in the bushes.

I am now that person in the supermarket queue, shamelessly telling strangers about my chafing woes. Them: “Lovely day”. Me: “It is, but I’m running later so I’ll need to be careful my shorts don’t rub…” Them: [instantly recoiling, abandoning their full trolley and swiftly exiting the shop].

Not that I care. A running silly billy doesn’t trouble themselves with social cues like someone repeatedly glancing at their watch or having an expression resembling Edvard Munch’s The Scream as you blether on undeterred about time splits and compression socks.

Read more: Why we all need to spring clean our minds

And I haven’t even started on my list of upcoming races yet … Ah yes, that’s another key indicator of silly billy runner status. When you will happily shell out hard-earned cash to run at a location that you could run at for free on the other 364 days of the year.

Other tell-tale behaviours include trotting in circles outside your front gate to round the distance up to the nearest mile or kilometre; buying special anti-chafing underwear; owning a medal display rack; calling food “fuel”; going to bed at 9pm sharp. It’s a slippery slope.