You better not shout, you better not cry, you better not pout, I'm telling you why - a big horned demon-faced creature carrying chains to beat you then carry you away to the underworld for a good drowning.
The creature, which looks far more like something you'd see in an episode of Buffy the Vampire Slayer or a Grimm Brothers tale than what you'd find on Christmas cards, has much more to do with St Nicholas and Germanic folklore.
Originating from Pagan times, this soulless, red-eyed monster is often depicted as a half goat, half devil creature with two enormous horns, long pointy sharp teeth and tatted furs who appears to have grown increasingly larger and more horrific in the 21st century thanks in part to US adoption, with Hollywood recently taking a stab at recreation with a movie starring Adam Scott.
While St Nick would reward good children by filling the shoes they left out with sweets, Krampus would swat bad ones with chains and take them back to his 'lair', a fate far nastier than our chubby old Santa's lump of coal.
This left children in parts of Europe in a sweaty terror on the nights leading up to Christmas, waiting for Krampus to peer through their bedroom window and swipe them from their beds, throw them into a cage attached to his back and carry them to their fate, which could be drowning, being eaten, or sent to hell.
If you want to experience the magic that is Krampus, strap yourself in for a Universal Studios Hollywood Horror experience, Euro-style, in the Austrian city of Salzburg. This fairytale-like town circles a mountain topped with a medieval fortress which is often dusted with snow at this time of year.
Beside the Salzach river, its tiny streets lined with baroque buildings fill with Christmas markets in late November which sell gingerbread and mulled wine to people gathering on its streets.
Come December 5, there's one small pocket in the back streets which holds a special celebration of its own.
On the night that Krampus is traditionally supposed to make his terrifying trawl through Europe's streets searching for bad children, a "Krampus run" is held.
Local men dress in Krampus costumes made at a nearby workshop with terrifying attention to detail, and run through the streets of Salzburg.
Expecting a Hollywood-type faux chainsaw-massacre event of epic proportions, I was more amused than afraid witnessing heavily-costumed Krampuses slapping passers-by on the posterior and stopping for selfies. However the runs can be unpredictable and what you'll see can vary on the year - from throned Krampuses with torches and flares to hundreds filling Salzburg's narrow cobbled lanes.
While Salzburg's run can be fairly innocent, things can get mean in other parts of Europe including smaller towns in Austria, Czech Republic, Slovenia, Germany and Hungary, where men, fuelled by a mulled wine or two, use the disguise and anonymity to do things they wouldn't normally do, which often involve chasing women.
Back in the US, Krampus-fever has taken hold, with parties and street parades being held in various cities and has earned itself the nickname "Halloween for adults".
Krampus' evolution can be explored at Salzburg's Christmas Museum, where proprietor Ursula Kloiber has amassed fascinating Krampus collectibles throughout the centuries, including pictures of him in soldier clobber dragging a couple of missiles during World War 1.
FIVE LESS TERRIFYING THINGS TO DO IN SALZBURG
Eat and drink your way through the streets of Salzburg over Christmas,which have been operating around Salzburg since 1491. Instead of retreating to their loungerooms by the fires during cold winter evenings, locals take to the streets to sip gluhwein (mulled wine) and eat raclette, Viennese sausages, pretzels, gingerbread and other warming treats.
Silent Night Museum
Little known fact: The song Silent Night was written and performed for the first time on 24 December 1818 in a tiny town outside of Salzburg called Oberndorf. A tiny chapel was built to commemorate this in 1937, followed in 2016 with a museum where you can learn about the area's history as well as given a complete overview of how the song was composed and performed. You can even create your own version at the museum's karaoke machine. stillenacht-oberndorf.com
One of Salzburg's most popular forms of entertainment is Winterfest, a dinner and performance from a young a circus troupe from Canada. Set in the Volksgarten under two big tops, guests are treated to a three courses unusually served in narrow glasses before being treated to a ninety minute performance of mind-boggling contortion and energy. The performances change regularly; check the website for details. winterfest.at
Experience cafe culture
There's no cosier place to while an hour or so away than a traditional Viennese coffee shop, where famous artists such as Mozart used to sip on hot chocolate doused with almond praline. You can do the same at Cafe Tomaselli, at 300 years old is Austria's oldest coffee house, which serves pretty good coffee even by Melbourne standards while apron-clad ladies whisk huge trays of delicious local streudels and Sacher tortes to tempt customers. tomaselli.at
Museum of Modern Art
Sharing space with its famous fortress on top of central Monchsburg Mountain, on a sheer cliff face overlooking the old town is an extraordinary setting of Salzberg's finest contemporary art. On the top floor is restaurant M32 which has views over Salzburg as well as some of the town's finest cuisine. m32.at/en; museummoderne.at
The Krampus run can change every year, up to the last minute: check Salzburg.info regularly for updates.
Thai Airways has four weekly direct flights from Bangkok to Vienna with connections from Melbourne, Sydney, Perth and Brisbane; thaiairways.com
You can catch a train to Salzburg from Vienna, which takes around 2.5 hours. Raileurope.com
Hotel Sacher offers traditional Austrian accommodation in a five star setting in the centre of town, as well as being the creators of the original Sacher torte. Sacher.com
Salzburg Christmas Museum, Mozartplatz 2, salzburger-weihnachtsmuseum.at. Entry €6 adults, €3 children. Open 10am to 6pm Wednesday to Sunday, closed from February 1 to March 14.
Kylie McLaughlin travelled as a guest of the Austrian National Tourist Office and Thai Airways.