Select the best one word substitute for the phrase: Very rude or coarse; vulgar.

Introduction / Context:
This question checks your understanding of precise adjectives that describe behaviour and language. The phrase given is very rude or coarse; vulgar, which is commonly used in social and literary discussions. You must select the word that most accurately captures this sense of something being offensive in taste or manners rather than simply referring to physical size or appearance.

Given Data / Assumptions:
- The phrase to be replaced is very rude or coarse; vulgar.
- Options: gross, adipose, porcine, corpulent, boisterous.
- Only one of these is primarily used to describe behaviour or language that is crude or offensive.

Concept / Approach:
The adjective gross has several meanings, one of which refers to something that is very unpleasant, rude, or vulgar, especially in taste, behaviour, or language. It can also mean total or overall, but in the context of this question, the behavioural meaning is clearly intended. The other options all relate more to body fat, animals, or noisy behaviour and do not match the specific idea of vulgarity. Therefore, gross is the most suitable one word substitute.

Step-by-Step Solution:
Step 1: Focus on the core idea of the phrase: rude, coarse, and vulgar behaviour or language.
Step 2: Recall the meanings of gross, adipose, porcine, corpulent, and boisterous.
Step 3: Match gross to this meaning, noting that it is often used to describe crude jokes or offensive behaviour.
Step 4: Eliminate words that refer mainly to fatness, animals, or loud energy rather than vulgarity.

Verification / Alternative check:
Consider a test sentence: His remarks at the meeting were very rude and vulgar. We can rewrite this as His remarks at the meeting were gross, which is natural and widely used. Replacing with adipose, porcine, or corpulent is meaningless here because those words describe physical fatness. Boisterous describes noisy and energetic behaviour and does not necessarily carry the idea of vulgar or coarse language. Therefore, only gross fits well.

Why Other Options Are Wrong:
- adipose: refers to fatty tissue; it is a biological term and has no connection with manners or speech.
- porcine: means relating to or resembling a pig; it is sometimes used metaphorically but does not specifically mean vulgar in the sense used here.
- corpulent: describes someone who is very fat or obese, again purely physical and not about rudeness.
- boisterous: means noisy, energetic, and cheerful; someone boisterous may be loud, but the word does not inherently mean vulgar or coarse.

Common Pitfalls:
Students sometimes confuse words that appear frequently in one context with broader meanings than they actually have. For example, knowing that corpulent and adipose relate to fatness may tempt you to choose them if you overlook the focus on rudeness and vulgarity. Vocabulary questions require paying close attention to the context implied by the descriptive phrase. Always ask yourself whether the candidate word would comfortably fit into a natural sentence about behaviour or speech, not just any property.

Final Answer:
The best one word substitute for very rude or coarse; vulgar is gross.