Lots of interesting questions and opinions here. Let's look at the law and what it really says for a minute.
First, the law says that it is illegal for a CHL to carry a firearm while intoxicated (PC 46.035). Note that it does not say while under the influence or while drinking. You must be intoxicated for this to come into play.
Also note that this chapter of the law does not define what is intoxicated. So, to find a definition, we must look elsewhere. The first place to look, is Chapter 1 for the main definitions. These definitions apply to the whole Penal Code unless they get overridden by a specific section or chapter definition. There is no definition of intoxication there either. OK, so there is no legal definition specifically in play here. Under the Code Construction Act, (chapter 311 of the Government Code) we find that words are used according to their normal usage unless there is a statute giving the word a technical legal meaning. So, we next look to see if there is a definition of intoxicated in any law, giving the Penal Code first priority. Fortunately, we find one in Chapter 49. This defines intoxicated as:
(A) not having the normal use of mental or physical faculties by reason of the introduction of alcohol, a controlled substance, a drug, a dangerous drug, a combination of two or more of those substances, or any other substance into the body; or
(B) having an alcohol concentration of 0.08 or more.
So we have one of two conditions that define intoxicated. The officer can either prove the person had a BAC over .08 or can prove he was not in possession of his normal faculties due to ingestion of a drug or alcohol. The easiest way is to take some type of BAC, such as a breathalyzer, a urinanalysis, or a blood test. Of course, the officer can ask the suspect to do this, but the suspect can decline with no penalty. As was stated, the implied consent law really only applies to driving. So, if you consent to a BAC or any test like this, you might be easily proven intoxicated - even though you are in full possession of your normal faculties (I know several alcoholics who are not affected until their BAC goes over about .20 or .25 and almost never have less than a .10).
But assume we cannot get you to agree to the test. How do I still prove intoxication? I can ask you to perform the field sobriety tests and base my testimony on that. Of course, we will assume you are smart enough to not take those tests either (you never have to take a field sobriety test). Then I go based on my normal observations of your condition.
Any officer out of the academy knows that there are generally four signs of intoxication that courts look for. The signs are bloodshot eyes, slurred speech, unsteady on the feet, and an odor of alcoholic beverage coming from the breath. If a person possesses one of these, it is not a sign of intoxication. If a person possesses any combination of three of these signs, it constitutes probable cause to believe he is intoxicated. (And no, I cannot cite the court case that made this ruling. It is just what I have been taught and used in court for the past 20 years. The new trainees I get are all being taught the same thing in the local police academies too.) Other things that help are signs like rapid mood swings, unusual attitudes, disorderly clothing (especially people who have either vomited or urinated on themselves).
This is how I can testify in court and prove you were intoxicated. I have had lawyers challenge these observations such as asking me if I knew how the client spoke before when he was sober (so how could I tell he was slurring or different). They have asked how I knew how the client normally walked, or if I have ever had bloodshot eyes from a lack of sleep. I will answer that any one sign of these could be explained away but not three or four together.
And TXI had one other point that is important. This is not the same standard as for PI. The PI standard is that he be so intoxicated that he may be a danger to himself or others (of course, possessing a gun while you are intoxicated makes the danger to others fairly easy to prove).
And here is a trick you might not be aware of that could really hurt you. If the officer books you for 46.035 carrying while intoxicated, be careful that he does not also book you for PI. Most PI cases are not truly heard or handled, but you are held until sober, then found guilty and sentenced to time served or such. If I were handling this type of incident, I would guarantee I would do this, because I could then use the PI conviction as proof that another court had FOUND that you were intoxicated at that point in time. Makes this case easy since there is a rule saying I only need to adjudicate any point one time.