Rinse the red chillies and pat them dry.
Slice them into rounds, removing the seeds if you want to reduce the heat.
In a saucepan, combine the vinegar, salt, and sugar.
Bring the mixture to a boil, ensuring the sugar and salt are completely dissolved.
Place the sliced red chillies in a clean, sterilized jar.
Pour the boiling vinegar mixture over the chillies, submerging them completely.
Secure the lid and let the jar cool at room temperature.
Once cooled, place the jar in the refrigerator. After 24 hours, your pickled red chillies are ready to enjoy.