c. Sarcastic or threatening remarks.
These should not be provided in a complaint letter. These are not relevant in filing a complaint. Putting said remarks in a letter will put the company or person-in-charge in a defensive position. They might be offended and instead of helping you with your complaint, they will then leave your concerns unattended.
It is better to simply use a civil or formal tone in your complaint letter. This way, the company you are complaining against will help you the soonest time possible to resolve the complaint.
