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The man I met was a smelly redheaded middle-ager.

Do I need a comma here after smelly?

It is really hard to post here because of the constant rejection of my question body or tags.

Whether or not you use a comma has to do with what type of adjectives you think you're using.

If you can either swap the position of the adjectives or put an and between them without altering the meaning, then you are using coordinate adjectives and should use a comma.

Take this as an example:

❔ It was a dark stormy night.

Do we need a comma?

✔ It was a dark and stormy night.

✔ It was a stormy dark night.

So, it uses coordinate adjectives, and a comma should be used:

✔ It was a dark, stormy night.

Note that you can always use an and instead of a comma. In this case, most people would probably use an and. But a comma is also fine.

But adjectives that cannot be rearranged or have an and inserted without changing the meaning should not use a comma:

❔ It was an exquisite custom houseboat.

✘ It was an exquisite and custom houseboat.

✘ It was a custom exquisite houseboat.

In this sentence, exquisite is directly modifying custom. (The custom houseboat was exquisite.) If the two words are separated or their position swapped, the meaning of what's being described changes.

Therefore, this is an example of cumulative adjectives, and there is no comma:

✔ It was an exquisite custom houseboat.

In some cases, it's not immediately clear what the meaning of a phrase is. Your own sentence is one of those.

It's not clear which of these you actually mean to convey:

1. He was a smelly middle-ager. He was also a redheaded middle-ager.
   This uses coordinate adjectives:
   
   → He was a smelly and redheaded middle-ager. OR
   
   → He was a smelly, redheaded middle-ager.




2. He was a redheaded middle-ager who was smelly.
   
   This uses cumulative adjectives:
   
   → He was a smelly redheaded middle-ager.

So, really, you just need to ask yourself if your sentence still works if you add an and between the adjectives. If it does, then you can either use an and or you can use a comma. (But you shouldn't leave it with nothing between the two adjectives.) On the other hand, if inserting an and changes what you want to convey, then don't use a comma.

My personal opinion is that I think it would sound a bit awkward with an and (or, therefore, a comma). If you really do mean them to be separate adjectives, I suggest rephrasing the sentence:

The man I met was a redheaded middle-ager. He also smelled.

Or something like that. But that goes beyond the scope of explaining the difference between the two types of adjectives.

The man I met was a smelly redheaded middle-ager. Do I need a comma here after smelly?
It is really hard to post here because of the constant rejection of my question body or tags.

I know this question is about an English sentence. It should be posted on the English Stack Exchange or the English Language Learning Stack Exchange. However, the title is way too broad: "Do I need a comma?"

The English language is a subject-prominent language. This is different from a topic-prominent language, such as Chinese, which may also explain why Chinese punctuation rules are quite different from English punctuation rules.

Deathblade is a translator of Chinese web novels, and he notices that there are a lot of commas in Chinese writing; in his translations, he has to replace the commas with periods, as well as insert subjects. In my own observation of Chinese-as-second-language users, they use a lot of periods with excessive use of pronouns. It is not necessarily wrong/unacceptable in Chinese, but it does feel very rough. In my own analysis of the writing, I notice that an English sentence is subject-prominent. It is literally SVO (subject-verb-object). When English speakers want to talk about a different thought, they begin a new sentence with a pronoun to refer to the subject in the previous sentence. Meanwhile, a Chinese sentence is topic-prominent. All the clauses in the sentence are about this topic. The topic is most prominent, and all the clauses are actually comments (topic-comment). While native English speakers may write in this format (subject-verb-object-comma-conjunction-subject-verb-object), native Chinese speakers may write in this format (topic-comment-comma-comment).

As a heritage speaker of Chinese, I'd say that I think more like a first-language speaker than a second-language speaker. Other heritage speakers may lean towards the second-language speaker side, because they associate more with their English-speaking friends than Chinese-speaking parents, or because they never went to school in China. At first, I didn't know how to describe it in words. Stories just read smoothly from the get-go, and I just copied this pattern. I also like to read stuff about linguistics, and the technical terms are really helpful in putting my feelings into words.

TLDR: Rules of punctuation depend on the language. English and Spanish are both subject-prominent languages and thus, in my opinion, have very similar punctuation styles. Chinese is a topic-prominent language, like Japanese and Korean, so the punctuation use for commas revolves around separating separate comments.