Workshop & Garage Etiquette
Approaching workshops, be they professional workplaces or someone's home garage, is an exciting time for car enthusiasts but, if you haven't spent much time around them it's important to understand there are a few basic ground rules we should keep in mind before we make ourselves at home.
I'm lucky enough to have been granted access to many workshops over the years, and after almost 25 years working in this trade, I think I'm in a fairly unique place to walk you guys and gals through the dos and don'ts of behaving in sheds. So, without further ado, here are The Golden Commandments of Garage and Workshop Life:

CURSING IS AN ARTFORM
Swearing when something goes wrong is an intrinsic part of garage and workshop life. Cursing the very soul of a part which won't come undone (or go in), a leak that won't stop existing, or raging at something which has broken is a time-honoured test of our spirit we undergo on any and all car builds.
Anyone can spit out a few F-bombs or C-bombs, but true workshop legends like Mechanical Stig understand the artform of cursing: be creative. You can't get the job you're trying to do finished when you're distracted by all the frustration and anger swirling around in your head, so take all that energy and get it out of your system by cursing the source of your aggrevation as a pack of slippery gypsies. Or a recreational botherer of barnyard animals. Or a pelican-touching, fart-sniffing, turd-taster that eats the pickles and buns off a burger but throws the meat away... ahem
You get the gist. Don't bottle the frustration up, and don't throw tools. Humans are the apex creatures on this planet, so use that big brain to come up with something humourous and spite-filled so you can clear your head and move on with your day.

CONSIDER OTHERS
If you're in someone else's garage or a professional workshop, before you go verbally blasting the mating habits of inanimate objects which are harshing your vibe, consider whether other people need to hear this. Workshops and garages can be testosterone-fuelled places but that doesn't give anyone a free reign to act like a primate; there can be kids, partners, grandparents, or other people who don't appreciate boorish behaviour within earshot or sightlines.
It should go without saying that a bit of light riffing of others is fun, but nobody should get getting treated like a lower-class, whether they're new to the game or an old hand. And this is especially important in the workplace - our hobby is under more pressure now than ever to exist so if we hack on all the apprentices who is going to be left to help us work on our old dinosaur nuggets when we're too old to crawl around under a car on jackstands, or bench-press a transmission in?
RESPECT
Everyone deserves respect as a human being, and this is especially true when we're dealing with workshops. No matter who they are, from the person answering the phone, to the boss who owns the workshop.
We can all get upset when our pride and joy is in a shop and something hasn't gone how we wanted, but yelling and screaming at a workshop employee isn't going to get your car back any faster or magically cure the problem you're dealing with. There's no shame in telling a shop you're disappointed at progress or the finished result, but try to remain calm and ask them to outline what happened that put you in this spot.
If you feel yourself getting upset, tell them. Tell them so they can understand how much this means to you, and that you'll go away to calm down and call back later (or visit if you can). Nobody gets anywhere or anything worthwhile when we're upset, and these cars mean a huge amount to us, so it's understandable but something we all need to manage ourselves.

BARRIER METHOD
This is basic. If there are signs saying "do not enter" on a workshop, don't. Look for the signs, too, as you need to be aware this is normally an insurance issue, but also professional workshops don't want randoms strolling in off the street, so your first port of call should always be to the front desk until you're invited onto the shop floor.
At a private garage if you haven't been invited directly to the garage it's also nice to be polite and respect the person's house by knocking on the front door rather than snooping around the side or back.
DON'T BE A GRUB
Try to be tidy. Having consideration for others extends beyond not getting drunk and being boorish when it's not appropriate, and you should try to keep someone else's workshop or garage tidier than your own - not only is this polite it's easier to work in, and safer too.
Keep your work area and tools tidy so nobody is tripping over you as they're moving around. Clean up spills when they happen to avoid slip-hazards. Think about how others are working around you - don't just start hammering the bejeesus out of the engine bay if someone is under the suspension without checking they're cool for you to do that.
Also, if you see the hand towels (or toilet paper) have run out ask someone where the spares are kept and change them.

