If I were to create the most onerous Tax code I could this is how I would do it.
1. I would make sure you couldn't escape it.
What is the point of collecting taxes if you can escape the tax.? Taxing cigarettes and booze is silly because if you want, you can not use those products. However, If I tax income, there is pretty much no way out of it. You have to earn money to live and if I tax your income you have very little way to avoid paying my tax, unless you were already wealthy and no longer had to earn income.
2. I would make sure you paid it even if you died
Nothing as certain as death and taxes right? I'm going to make sure taxes are even more certain. When you die, I am going to tax your estate. You are dead, you won't need the money. Leaving it to your heirs? Please, everything you have is mine.
3. I would make sure you paid it on income you didn't even really "earn"
I don't care what form of "income" you have. If someone gives you a gift, I'm going to tax it. If you win a new car, that is making you better off (and is therefore income) so I'm going to tax that too.
4. I would make sure you didn't know how much you were paying
Before you even get your paycheck, I'm going to take my share of it. Knowing human nature, I know if you never see it you won't realize how much in taxes you are paying. Further, I'm going to tax other things like Corporate income and the like. You won't ever directly see the cost of this since this will only raise the price you pay for goods. Ingenious!
5. I would make sure the burden would be placed directly on you to comply with my plan
My tax plan probably needs to be really complex to make all of this work and make sure I can extract all the money I can from you. But no way do I want to take the time to figure out what you owe me; I'll leave that up to you. Therefore I'll pick a date, say April 15th (or maybe the 17th if the 15th is on a Saturday), that you will be responsible for figuring out how much money you should have given me. If you should have given me less, I'll give you some money back (interest free of course). However if you screw up you will get stiff penalties and I will force you to pay me that and the taxes you owe me (with interest).
6. I would make sure it was so horribly complex you would never understand it
If you actually are able to understand how to comply I might not get all the money I need from you and you may find ways to pay less. Further, the more complex I make it the easier it will be for me to change it and get more money from you.
7. I would make sure I could easily change the plan to extract even more taxes from you
I would probably change some part of the tax code every year. I might change the tax on things like dividends to make them more attractive. I might change the tax brackets or remove various deductions. The code will however be so complex and so esoteric that you won't even bother to really understand it and just pay me whatever I tell you to pay me.
8. I would make sure I could lower the taxes for my friends while at the same time thinking you are getting the better deal.
I would do things like create tax breaks that seem to work for the common man but in reality they work best for my rich friends like myself. I could probably implement this by doing something like allowing you to deduct interest on a big ticket item. Say your house. Of course, you won't be able to get full benefit out of this because you won't really spend more than your standard deduction. However, my rich friends, with big houses and mortgages, and with multiple houses on top of that, will benefit far more than the average person. The average person won't realize that they are paying for my rich friend's tax break. They will only see their relatively small deduction and feel good about it. Given their lack of understanding of my tax code, they will fight tooth and nail to save this deduction all the while not realizing how much they are really paying to have it.
9. Even if you try to leave the country, I will still make you pay the tax
I will decree that even if you leave the country to try and avoid my tax, your rightful duty as a citizen is to pay me the tax. I don't care if you work in a foreign country for 20 years, if you are a citizen of my great land it is your duty to pay me the tax.
Sounds awful doesn't it? I'm glad this system doesn't really exist.