Θέλω πλάκα, όχι καβγά.

Because καβγάς is the dictionary form, the nominative singular: ο καβγάς = the quarrel/fight.

After θέλω (I want), the noun is the direct object, so Greek uses the accusative:

• ο καβγάς → τον καβγά

Since there is no article here, you just see the noun form by itself:

• Θέλω καβγά = I want a fight/quarrel

So in Θέλω πλάκα, όχι καβγά, καβγά is accusative singular.

Greek often leaves out the article when talking about something in a general or indefinite way.

Here the speaker is not talking about:

• the specific joke
• the specific quarrel

They mean something more like:

• fun / joking around
• a quarrel / conflict

So the article is unnecessary.

If you added articles, the sentence would sound more specific:

• Θέλω την πλάκα, όχι τον καβγά
  This would suggest a more specific context, not the general idea.

Because όχι and δεν do different jobs.

• δεν negates a verb
• όχι means no / not and is often used for contrast, especially before a noun or phrase

Here, the speaker is contrasting two things:

• πλάκα
• καβγά

So όχι is exactly what Greek normally uses:

• Θέλω πλάκα, όχι καβγά.

If you wanted to use δεν, you would usually repeat the verb:

• Θέλω πλάκα, δεν θέλω καβγά.

Both are natural, but the original sentence is shorter and punchier.

In this sentence, πλάκα means something like:

• fun
• joking
• messing around
• banter

It does not necessarily mean one single joke.

This is a very common Greek word with several meanings depending on context. For example:

• κάνω πλάκα = I’m joking / kidding around
• έχει πλάκα = it’s funny / it’s fun

So here Θέλω πλάκα is more like:

• I want fun
• I want joking around
• I want banter, not a quarrel

Yes, it is singular.

But Greek often uses a singular noun to express a general idea, just like English does with words such as fun.

So πλάκα here does not mean one joke in a strict counting sense. It means the general idea of joking/fun.

If you used the plural πλάκες, it would sound more like:

• jokes
• funny tricks / pranks
• multiple countable instances

So singular is the natural choice in this sentence.

πλάκα is also in the accusative, because it is the object of θέλω.

The reason it looks unchanged is that for this noun, the nominative and accusative singular have the same noun form:

• η πλάκα = nominative
• την πλάκα = accusative

Without the article, both simply appear as πλάκα.

So both nouns in the sentence are objects:

• πλάκα = accusative
• καβγά = accusative

Yes. Greek word order is more flexible than English word order.

The version you have:

• Θέλω πλάκα, όχι καβγά.

is natural and straightforward.

But you could also say:

• Πλάκα θέλω, όχι καβγά.
  This puts more emphasis on πλάκα.

Or:

• Καβγά δεν θέλω, πλάκα θέλω.
  This gives a stronger contrast.

So the original order is neutral and natural, but other orders are possible for emphasis.

A rough pronunciation guide is:

THÉ-lo PLÁ-ka, Ó-hi kav-GÁ

A few useful pronunciation points:

• θέλω: θ sounds like th in think
• όχι: χ is not an English h exactly; it’s a Greek throat/fricative sound
• β in καβγά is pronounced v
• γ before α is a voiced soft sound, a bit like the Spanish g in lago for many learners

The stress falls on:

• Θέλω
• πλάκα
• όχι
• καβγά

It sounds natural and colloquial.

It is short, direct, and very speech-like. A native speaker could absolutely say this in conversation.

It has a slightly emphatic tone, almost like:

• I want fun, not a fight.
• Let’s joke around, not argue.

So it feels everyday and idiomatic, not artificial.

The comma marks a pause and highlights the contrast:

• πλάκα
• όχι καβγά

It works a lot like English:

• I want fun, not a quarrel.

In short contrastive sentences like this, the comma is very natural. It helps the sentence read the way it would be spoken.

Without the comma, the meaning would still be understandable, but the punctuation with the comma is better and more standard here.