tl;dr– A gross mistake in programming is like a "critical" bug in that it's a mistake not falling into a lesser category. Assuming that the speaker was expressing an objective point, I wouldn't take it as rude at all.
Gross things aren't easily described in limited terms.
Gross is when something evades description as a limited subset of a conceptual framework.
For example, "Orders of magnitude (length)", Wikipedia, has a neat comparison showing the relative sizes of things. Including this image.
After looking at those sizes, how big is a planet? How about a star? A solar-system? A galaxy? A galaxy-cluster? Or, the observable universe?
Those things aren't all of maximum size. In fact, a planet can be utterly tiny compared to other objects. Still, when folks are talking about sizes, even a planet may be so large as to evade description as being of a size other than the maximum a person would generally conceptualize. And so, all of those things are grossly large.
Examples of how things can be gross.
Some common areas of usage:
| Encompassed/saturated space |
Examples |
Effective meaning |
| Quantifications |
Gross income, gross revenue, gross weight, GDP (gross domestic product), gross sales, gross salary, gross volume, gross count, gross rate. |
The most encompassing version of the quantification, without exclusions. |
| Qualifications |
Gross misconduct, gross negligence, gross rebellion, grossly justified, grossly deserved, gross departure. |
The qualification applies strongly, beyond limited notions of the qualification. |
| Sensory perceptions |
Gross scent, gross image, gross feeling. |
Overwhelming to the senses (which is usually unpleasant or/and disruptive). |
Usually, ideas don't saturate the conceptual-frames in which they're discussed. However, when they do, they're "gross".
Examples:
| Concept |
Normal (not necessarily "gross") |
Gross |
| Income |
Some notion of incoming gains. |
The fullest notion of income. |
| Mistake |
Some deviation from properness. Often mistakes can be described as having a type and degree. |
Overflowing deviation from properness. May defy explanation as a single type of mistake or/and be extreme in degree. |
| Taste |
Some departure from the background sensory perception of "no taste". Often taste can be described as having a type an degree. |
Overflowing deviation from background. May defy classification as a type or be extreme in degree. |
Because grossness is about encompassing/saturating a conceptual space, it can be pretty subjective.
However, folks generally find things that saturate their conceptualizations to be unpleasant. There are strong feedbacks between conceptualization and acceptance:
Accepting something promotes conceptualization of it.
Lack of conceptualization drives rejecting something.
Note that repeated exposure expanding conceptualization is called desensitization, which tends to shift perceptions away from grossness.
Which gets into the difference between grossness and badness. For example, someone may not care for the taste of something common-but-undesirable, e.g. stale bread, though such tastes wouldn't really be "gross".
Regarding "gross mistakes" in the OP.
The context: my colleague accidentally spotted errors in certain programming code and tried to inform the maintainers of the code. He wrote a request as follows: "Tests are written with numerous gross mistakes. For example" and then few excerpts of the code followed.
It seems to me that in the given context "gross" can be interpreted as "disgusting", while "mistakes" sounds accusing despite the wrong code may be not their fault.
A gross mistake is a mistake that isn't easily described as a lesser sort of mistake. This is, it's a mistake of maximum extent in the speaker's conceptual-framework.
By analogy, say you have a bug-reporting system, where you classify all bugs as Minor, Small, Normal, Large, Major. Here, the OP was saying that they found numerous bugs in the Major category.
I'll be grateful if you prove or disprove my understanding of the phrase's tone and rate its rudeness 1 to 10.
Assuming that they were being honest, it wasn't rude at all; 0/10.
By analogy, it's like a teacher giving a student an F on an assignment on which the student makes sufficiently many mistakes as to be graded an F according to the normal grading scale. In that, sure, the student may not be happy about that result, but it's not reasonable to say that the teacher was being rude in objectively assessing the student's work.