flat tax? Yes, but you'd need other taxes too.
LUXURY TAXES MOTHER FUCKER
SIN TAXES BITCH
YOU WANNA GET FUCKED UP? DRINK SOME BEER? Pay a premium on that shit. Same with cigarettes. And fast food. And fooRAB high in fat content. And shit that's pre-processed garbage. We might as well try to at least encourage a healthier society since that'd save us money elsewhere.
Luxury taxes on items in certain price ranges. You want to buy a $1-$24,999 car? Pay X tax rate. Your car costs $24,999-$44,999? Well, you'll pay a little more. Anything over that amount? Have it an even higher rate for anything on up. Now, I say 'higher' because that's relative to whatever the fuck X would be. Also, you could change the brackets around on that sort of shit to find what would work best without hampering auto sales (which woulc happen to cars at the bottom of the brackets).
Hell, have other 'luxury' taxes for classes of items based on certain amounts. IE: you spending some money on jewlery? pay a little bit higher tax rate than the flat rate. Stupid shit for your car like rims? or a stereo? Extra tax. TVs over a certain amount? Extra tax. They're luxuries, they'd be taxed accordingly.
While flat would be great, additional rates would just add onto the flat rate and would be probably require much, much, much more.
lastly, an internet sales tax