Learn Dutch: Ik erger me aan het gedrag. - I am annoyed by the behaviour.

In Dutch, the verb zich ergeren (to be annoyed) is a reflexive verb. This means it acts like the subject is doing the action to itself, translating literally to "I annoy myself." Because the subject is Ik (I), you must use the matching reflexive pronoun me.

Why do we use the preposition aan here instead of a word for "by"?

Many Dutch verbs have fixed prepositions that don't directly translate to English. The verb zich ergeren always pairs with aan to indicate what is causing the annoyance. So, "to be annoyed by" translates as zich ergeren aan.

Could I use mij instead of me in this sentence?

You will almost always use me here. Mij is used when you want to put strong emphasis on the pronoun. Because a reflexive pronoun just refers back to the subject, it usually doesn't carry extra emphasis, making the unstressed me the natural choice.

How can I remember that gedrag (behaviour) uses het instead of de?

Nouns that start with the prefix ge- (and do not end in -ing) are almost always het words in Dutch. Another common example is het gebouw (the building).