My question involves criminal law for the state of: Texas
On the night of December 31st 2009, I arrived home from work around 8:30 pm. I was waiting on my roommate to get home as he was to be the driver that night when we went to a get together a friend was having. My roommate was arrested for a DUI earlier in the year and had a breath interlock on his car, which is why he does not drink anymore and was our designated driver (figured this was the fail safe method of going out/getting home safe for new years). I had one beer before he arrived and we set out. It was him, his girlfriend and I. As we headed to our friend's house, we were pulled over due to my roommate not having his front license plate on. It turns out that he was driving outside the provisions of his occupational license (unknown to me at the time) and was arrested on the spot for driving on a suspended license. The officer then asked his girlfriend if she had anything to drink and she said she had a glass of wine with dinner. He then looked at me (I was in the back seat) and said he could already tell I had been drinking (maybe I looked tired from working all day? not sure why I would look drunk off one beer). I did not deny it but I don’t remember admitting it. He then placed my roommate’s girlfriend under arrest for public intoxication. I was obviously upset that she, and soon I, were being arrested. I started to ask how you can be arresting us and his partner started to get in a defensive posture (i.e. hand on gun) as he took her to the back of his car. I was in no way resisting, simply asking why. The arresting officer then took me out from the backseat of the car and started to turn me around to cuff me and I asked why again at which point he started to get "firm" with me and be more "forceful" with cuffing me. I said I am not resisting (never did in any way), just want to understand why I am being arrested for public intoxication when I’m not in public nor am I intoxicated. He said it was for my protection. So I asked "protection from what?" and he responded "I’m protecting you from yourself". This is all recorded on a dash cam which I am using the freedom of information act to acquire. At this point I was placed in the car and we were jailed for 17 hours. At this point I have been to court and plead not guilty. The prosecutor tried to get me to plea out for smaller fine/community service and I said no. So I have elected for a trial by jury. My questions are, how is this even a remotely legal arrest? Can I win this in court? Can I represent myself and win or should I have a lawyer?
This has to be the stupidist waste of my time, the courts time and the tax payers money. I know the law states "(a) A person commits an offense if the person appears in a public place while intoxicated to the degree that the person may endanger the person or another." How does this even come close to applying to my case; being in the backseat of a car (public) after having had one beer in the past 2 hours (intoxicated). Any help would be great. Thanks!

