
sich aufregen (über/wegen)
to get upset
To become emotionally agitated, angry, nervous, or worried because of a person or thing.
Bitte reg dich nicht wegen dieser Kleinigkeit so auf.
Please don't get so upset about this little thing.
to upset / excite
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to get upset
To become emotionally agitated, angry, nervous, or worried because of a person or thing.
Bitte reg dich nicht wegen dieser Kleinigkeit so auf.
Please don't get so upset about this little thing.

to upset
To make someone emotionally agitated, angry, nervous, or worried.
Die ständige laute Musik von den Nachbarn regt mich furchtbar auf.
The neighbors' constant loud music really upsets me.

to excite
To create excitement, great curiosity, or anticipation in someone.
Die Ankündigung des Konzerts hat die Fans sehr aufgeregt.
The announcement of the concert really excited the fans.
'Aufregen' (to upset / excite) is a separable verb made up of 'auf' (up) and 'regen'. The old verb 'regen' means 'to move' or 'to set in motion'. So 'aufregen' literally means to 'stir up' feelings or set them in motion.
Diese Ungerechtigkeit regt mich wirklich auf.
This injustice really upsets me.
The prefix 'auf' is separable and goes at the end in a main clause. In the infinitive with 'zu', 'zu' goes between 'auf' and 'regen'.
Sein unhöfliches Verhalten regt viele Leute auf.
His rude behavior upsets a lot of people.
Distinguish carefully: 'sich aufregen' (to get upset) is reflexive and means that you yourself become angry or nervous. 'Jemanden aufregen' (to upset someone) is transitive and means that a person or thing triggers these feelings in another person.
Ich rege mich über die Verspätung auf. (Ich werde wütend)
I get upset about the delay. (I become angry)
When you get upset about something, the reason is usually given with the preposition 'über' and the accusative. The preposition 'wegen' (+ genitive/dative) is also possible, but 'über' is more common.
Er hat sich furchtbar über die schlechte Note aufgeregt.
He got terribly upset about the bad grade.
'Aufregen' (to upset / excite) can mean both negative emotions (anger, worry) and positive ones (excitement, anticipation). The context makes clear what is meant. The related adjective 'aufregend' almost always means 'spannend' (exciting) or 'exciting'.
Die laute Baustelle regt mich jeden Morgen auf. (negativ)
The loud construction site upsets me every morning. (negative)
to inspire / enthuse
Both verbs can express a strong positive reaction to an event. „Begeistern“ shows clear joy and enthusiasm, while „aufregen“ here mainly means creating excitement, curiosity, or anticipation and does not necessarily imply approval. „Begeistern“ is suitable for great joy, while „aufregen“ is more suitable for eager anticipation.

Der neue Film regte das Publikum mit seinem spannenden Ende auf.
The new film excited the audience with its thrilling ending.
Der neue Film begeisterte das Publikum mit seiner lustigen Geschichte.
The new film thrilled the audience with its funny story.