Ikke vær slem.

Because this is a negative command. In everyday Norwegian, negative imperatives are very often formed as:

ikke + imperative

So you get:

• Ikke vær slem
• Ikke gjør det
• Ikke løp

You can sometimes see Vær ikke slem, but Ikke vær slem is the more natural everyday order.

Because vær is the imperative form of å være.

A few forms of å være are:

• infinitive: å være
• present: er
• past: var
• imperative: vær

So:

• du er snill = statement
• vær snill = command/request

This verb is irregular, so the imperative is not something you can guess from er alone.

It is understood, but not stated. Norwegian imperatives usually leave out the subject, just like English often does.

So Ikke vær slem has an implied:

• du if speaking to one person
• dere if speaking to more than one person

The sentence does not need to say the subject explicitly.

Because adjectives in Norwegian often agree with the subject.

Here, the implied subject is one person, so slem is the normal form.

Compare:

• Du er slem = one person
• Dere er slemme = more than one person
• Barnet er slemt = neuter singular noun

So if you were talking to several people, you would often say:

Ikke vær slemme.

Slem can mean things like:

• mean
• naughty
• unkind
• badly behaved

The exact shade depends on context and tone of voice.

Very often, slem is used with children, where it can sound like naughty rather than seriously cruel. With adults, it can sound playful, mildly scolding, or genuinely critical, depending on the situation.

Yes, that is possible, and people will understand it.

But in ordinary spoken Norwegian, Ikke vær slem is usually the more natural way to give a negative command. Vær ikke slem can sound a bit more formal, literary, or marked.

So as a learner, Ikke vær slem is the safer everyday pattern to remember.

A rough approximation is:

• ikke ≈ IK-keh
• vær ≈ something like vair, but with a Norwegian r
• slem ≈ slem, with e like in bed

A few notes:

• ikke has a clearly pronounced double consonant
• vær has a long vowel
• pronunciation varies somewhat by dialect

Not automatically. It depends a lot on tone and who you say it to.

It can sound:

• normal and parental when said to a child
• playful between people who know each other well
• scolding or harsh if said sharply
• a bit inappropriate to a stranger unless the situation clearly calls for it

So grammatically it is simple, but socially the tone matters a lot.

Yes. This is a very useful pattern.

Examples:

• Ikke gjør det.
• Ikke kom for sent.
• Ikke vær redd.
• Ikke glem nøklene.

So if you want to make a command negative in everyday Norwegian, putting ikke before the imperative verb is a very common strategy.

Both are possible.

• Ikke vær slem. sounds calmer or more neutral in writing.
• Ikke vær slem! sounds stronger, more emotional, or more urgent.

So the punctuation changes the tone more than the basic meaning.