You've clocked that they're always at the vending machine, you've noticed them arriving at work looking a little bright-eyed and puffy faced, and one time you wanted to tell them they'd put their jumper on back to front.
You have an inkling your work colleague is a bicycle commuter - but you've never seen them arrive at the same time as you, and saying: "You look a little scruffy - arrive by bike?!" doesn't seem entirely polite. So how to be sure?
Here are the tell-tale signs that your buddy from across the room is a cycle commuter...
Always has a second breakfast - usually porridge
Many of your colleagues arrive at work and settle down to breakfast at their desks - but the commuter is probably loudly commenting that this is actually breakfast number two - unless they're exceptionally disciplined and good at that whole 'fasted riding' thing (in which case their bowl will be HUGE).
It's also usually porridge - the perfect post-ride mix of carbs and protein (provided it's made with milk) - with some sort of yummy topping that has special health benefits. 'Cos we cyclists know how to look after ourselves.
Once mysteriously had no shoes for a day
Most cycle commuters have been there at some point - the causes of socks-at-work day are:
1) Just forgot to pack shoes
2) Thought shoes were under desk, forgot took them home on 'drive day'
3) Couldn't fit shoes into backpack and decided shoes not actually that important as a component in life
They moan about stairs
But don't cyclists have strong legs?! Yes - strong, tired legs... strong, tired legs that would rather save themselves for bagging QOM's on the way home...
Bleeps, beeps and charging devices
You notice a reoccurring pattern - around five minutes after your potential commuter arrives into the office, there's a very familiar 'bleep, bleep' that reminds you of the sound your cycling computer makes when you stop at the lights.
Has adopted a funny winter walk in the morning
Most roadies will start wearing overshoes or even cycling specific winter boots as the temperatures drop, but a lot of commuters like to avoid the 'missing shoes' scenario above by simply wearing their day shoes on the bike.
This works out wonderfully, except that those shoes might not be so insulating. If you've noticed your suspect commuter is hobbling a little for the first 30 minutes of the day, they may well be suffering from 'cold foot'.
They're addicted to weather forecasts
You notice that around 4 or 5 pm, they begin to look out the window a little more frequently and that there is a weather forecasting site open in their tabs at all times.
They seem to receive a lot of parcels
At first, you thought this person just ordered a lot of stationary - then you spotted the tell-tale orange logo of that very popular online cycling retailer...
Eats lunch at 12 pm ON. THE. DOT.
It's generally not considered normal etiquette to eat lunch before 12 pm - but since cycle commuters are always hungry, they'll probably be the first racing to the kitchen when midday strikes.
They're usually smiling and rarely sick
Granted, intense exercise can lower your immune system - but regular gentle exercise generally means fewer sick days which is why encouraging cycling is something that could save employers thousands.
Since those who exercise regularly get to enjoy equally regular rushes of endorphins, your new commuting buddy is probably more cheery than those who spend time queuing in traffic each morning, too.
Failing all of the above - you could just ask them, then you can have a good natter about all the experiences you had when you first started commuting...