There are a lot of things tyrannical that the government has done, but since you challenged me name one, I'll name the worst of the worst. The National Defense Authorization Act for Fiscal Year 2012, which Obama signed, allows the President to use the military to arrest and detain American citizens on American soil indefinitely, and without due process of law.
I know that is incorrect because it directly violates the 5th, 6th, 10th and if taken from their home the 4th amendment. In which case this isn't Obama's fault but combined congress AND the Judicial Branch's fault for or recognizing this (which is impossible because even your party is involved in this).
You also misunderstand the act. It applies to those suspected of terrorisim, which admittedly vague doesn't mean they can arrest anyone they want. Also it doesn't affect you unless you are related, suspected, or direct involved with terrorist acts. The government would waste its time trying to detain its own citizens, that is idiotic, furthermore our CIA is very good at its job, like as good as the FDA is at quarantining a disease before it spreads good.
Edit* @Link, That bill has yet to be signed. And will not reverse the law of the previous bill, rather change it so that it gives a trial by the military, (a very high federal trial)