As an important family of metalworking processes, the many forms of welding are practiced by plenty of folks on a daily basis. Some of them are responsible for metal joining operations in construction or repair or fabrication or assembly; they're listed as welders on the payroll, and they generally know what's up with molten steel. Some folks use a buzzbox in their line of work from time to time, and can lay a bead on a broken frame or a cracked machine base, but don't weld full-time. And others strike arcs on their own time, and they work on their boats and trailers and sculptures and whatever else is around. But whatever the setting, there are two deep-seated urges common to almost all welders (including myself). The first is to swear a whole lot (I mean like serious goddamn Pulp Fiction-level shit, not like the bitch-ass cussing you hear from those limp-dick wannabe riveter bastards but manly fucking heartfelt profanity). And the second is to offer unsolicited opinions on the skill of other welders, which frequently involves the first.
The American Welding Society has established a whole bunch of standards relating to the quality of welds, and a whole lot of standards relating to the destructive and nondestructive testing of such. They use a lot of nice words like "porosity", "undercut", "slag inclusion" and "incomplete fusion". And these are really useful to engineers and inspectors and other such people who wear ties to work and listen to* safety labels, but for those doing the actual work they're largely unnecessary. A good welder can look at a shit bead and understand why it's shit and immediately know what machine settings and operator procedures need to be changed to make it not shit - at no point do the words "insufficient filler rod penetration" need to be spoken, and they usually slow the process.
So instead of a dry technical analysis of defects, which really don't paint a satisfying mental image of the weld, things are usually described with copious amounts of profanity. The AWS recognizes the GTAW ("tungsten inert gas welding"), GMAW ("metal inert gas welding") and OAW (plain ole "gas welding") processes. Welders themselves recognize a few additional ones - namely, "tungsten inert ass welding", "metal inert ass welding", and plain ole "ass welding". Of course, sometimes "ass" doesn't quite suffice - in the case of an exceptionally poor job, the term "dog ass" may be required. And it frequently is - a lot of underpaid Chinese kids learn things as they go because nobody gives a damn about training, and their practice pieces end up being your El Cheapo tools. But at least they have men with guns to look at their work and correct any mistakes - the same cannot be said of much "hobby welding".
Don't get me wrong - just because someone isn't formally certified doesn't mean they can't weld. And just because someone hasn't worked thirty years on the pipeline doesn't mean they're a clueless microwire meathead who doesn't know his stinger from his pecker - but sometimes it does, and more competent welders often have to grind out and re-fit the welds of these hoopty half-assers. Which is where the term "dog shit" comes into play. It's about as bad as you can get - a dog ass weld is fugly but it gets the job done, whereas a dog shit weld is both an eyesore and a safety hazard. It can be caused by any number of factors - a lack of training ("which one is the ground clamp?"), poor equipment ("it didn't come with a ground clamp!"), hooptiness ("I'll just use the jumper cables from my truck") or simple apathy ("fuck it, nobody's going to see this anyway"). But it's usually more than one of those things, and frequently all of them.
Of course, if there's one thing welders hate more than riveters, it's following any sort of consistent rule (hence the wildly differing classifications for every type of filler rod), so I wouldn't swear by the "ass"/"dog ass"/"dog shit" distinction. Sometimes you'll hear "dog fuck" and "shitcock" and "bitchtit" - much like there's no limit to how badly someone can fuck up a basic flat-position groove weld on A36 mild steel (let alone overhead fillets on stainless), there is also no limit to how much profanity someone can use to describe these fuck-ups. I have heard the undercarriage of a trailer described as a "fucking god-damn cocksucker piece of pissed-up fucking stupid-ass shit".
An emphatic "FUCK" conveys emotion well when compressors drown out the subtle nuances of intonation. And because most welding is done on industrial-zoned parcels far from the ears of women, children and the clergy, there's rarely anyone around to be offended by it. So go wild, and get creative - the more you swear at the work, the more difficult it will appear to laymen, and the more impressed they will be with your low rates. But don't get carried away. Swearing too much will just make you seem frustrated and incompetent, and excessive yelling usually creates more irritation that it dispels. Hot metal is best worked with a cool head. Don't be an asshole. E6013 electrode rods suck.
* Reading the safety labels is important, and everyone ought to do so before trying to operate a machine. But actually following the instructions contained therein is usually a futile exercise in overkill - "8 FEET FROM ANY FLAMMABLE MATERIAL OR SOURCE OF IGNITION", my ass. Acetylene tanks are made from quarter-inch armor plate, you could put a fucking cigar out on the fusible plug and nothing's going to happen 99 times out of 100** - not that I'd do it, but you could, and it wouldn't put you in anywhere near as much danger as the manual would like you to believe. That said, common sense is pretty goddamn important too, and there are plenty of people who think "it's faster this way" is a legitimate reason to disable safety controls, and these people are to be avoided at all costs.
** Don't actually put a cigar out on a fusible plug. It's really stupid. Don't be stupid. That's really the only safety warning anyone ever needs.