Learn Icelandic: Ekki vera að styðjast við marmarann!

The phrase ekki vera að followed by an infinitive creates a continuous prohibition. While ekki styðjast is a general rule meaning "do not lean", adding vera að implies the person is already doing the action and you want them to stop right now. It translates best to "stop leaning" or "do not be leaning".

Why is the infinitive vera used here instead of the imperative vertu?

In Icelandic, negative commands are formed using ekki plus the infinitive form of the verb. Even though a positive command would use the imperative form vertu, the negative form must always be ekki vera.

Why does the verb styðjast end in -st here?

This is the middle voice of the verb styðja, which means "to support". When you add the -st suffix, the action becomes reflexive. Instead of supporting an external object, you are supporting yourself, which translates to "leaning" in English.

Why is the noun marmarann in the accusative case?

It is determined by the preposition við. This preposition can take either the accusative or dative case depending on the context. When it refers to physical contact or leaning "against" something, it requires the accusative case.