Ne pijem toliko kave kao on.

In Croatian, ne is the normal negative particle, and it usually goes directly before the verb:

• pijem = I drink / I am drinking
• ne pijem = I do not drink / I’m not drinking

So pijem ne would be wrong here.

Pijem is the 1st person singular present tense of piti (to drink).

So:

• ja pijem = I drink
• ti piješ = you drink
• on/ona pije = he/she drinks

Croatian often leaves out the subject pronoun ja, because the verb ending already shows who the subject is. That is why the sentence says pijem, not ja pijem, although Ja ne pijem toliko kave kao on is also possible for emphasis.

This is one of the most important things to notice in the sentence.

After words of quantity like toliko (so much / that much / as much), Croatian usually uses the noun in the genitive:

• toliko kave = that much coffee
• puno vode = a lot of water
• malo vremena = a little time

The basic form is:

• kava = coffee
• genitive singular: kave

So:

• pijem kavu = I drink coffee
• pijem toliko kave = I drink that much coffee / that much of coffee

In other words, kavu would be the regular direct object, but kave is used here because toliko creates a quantity expression.

Here toliko means so much / that much / as much, depending on context.

In this sentence, because it is followed by kao on, it means:

• not as much coffee as he does

So the pattern is:

• toliko ... kao ... = as much ... as ...

Examples:

• Ne radim toliko kao ti. = I don’t work as much as you.
• Ona ne jede toliko kruha kao ja. = She doesn’t eat as much bread as I do.

Because on is the normal form used here after kao in this kind of comparison.

• on = he
• njega = him

In English, people often say as him in casual speech, but standard English prefers as he does. Croatian works similarly here: kao on is the normal comparison form.

The full idea is really:

• Ne pijem toliko kave kao on pije.
• I don’t drink as much coffee as he drinks.

Since pije is understood, Croatian usually shortens it to kao on.

Yes, you can think of it that way.

The full sentence could be:

• Ne pijem toliko kave kao on pije.

But Croatian, like English, often leaves out repeated material when it is obvious:

• Ne pijem toliko kave kao on.

This is completely natural and very common.

Compare in English:

• I don’t drink as much coffee as he does.
• I don’t drink as much coffee as him.
  (common in casual English, but not the best match for Croatian grammar)

So in Croatian, kao on is a shortened comparison where the verb is understood.

If you said only Ne pijem toliko kave, it would mean:

• I don’t drink that much coffee
• or I don’t drink so much coffee

That is a complete sentence.

But when you add kao on, you introduce a comparison:

• Ne pijem toliko kave kao on.
• I don’t drink as much coffee as he does.

So on tells you who the speaker is being compared to.

Yes. That is grammatically correct.

• Ne pijem toliko kave kao on. = neutral, natural
• Ja ne pijem toliko kave kao on. = I don’t drink as much coffee as he does

Adding ja puts extra emphasis on I. Croatian often drops subject pronouns unless they are needed for contrast, emphasis, or clarity.

Because piti is imperfective, and it is the normal choice for habitual or general actions like drinking coffee.

• piti = to drink in a general, ongoing, repeated sense
• popiti = to drink up / finish drinking a specific amount

So:

• Pijem kavu svaki dan. = I drink coffee every day.
• Popio sam kavu. = I drank/finished the coffee.

In Ne pijem toliko kave kao on, the meaning is about a general habit or amount, so piti is the right verb.

Croatian word order is fairly flexible, but this sentence is already in the most natural order.

• Ne pijem toliko kave kao on.

This sounds normal and neutral.

Other orders may be possible in special contexts for emphasis, but they are not the best choice for a learner. If you are starting out, it is safest to keep this exact pattern:

• ne + verb + toliko + noun (genitive) + kao + person

For example:

• Ne jedem toliko kruha kao ti.
• Ne radimo toliko kao oni.

So this sentence is a very good model to copy.