If you accuse your parents of being tyrants, you are saying they abuse their control of you — they are cruel, overly restrictive of your freedoms, and unfair. A tyrant is a ruler who is cruel and unjust.
Here's an idea for a game: list all the tyrants in history and vote for the worst tyrant of all time. Don't limit yourself to 20th or 21st century ones like Hitler and Stalin and Saddam Hussein. Maybe put Attila the Hun on your list. You could also name a few minor tyrants in your life, such as your boss or another person with unreasonable demands.