That's a lot to unpack, holy crap.
Neither of those is psychoactive or a drug, though absinthe could be considered both and may be lumped in with alcohol since its also a drink.
For something to be psychoactive it must have "mind altering effects," which would include things like hallucinations.
Caffeine is technically a stimulant, but not a very strong one. Unless you're abusing energy drinks or taking caffeine pills, or have a caffeine sensitivity, its not a big deal.
Alcohol is technically a depressant when referring to recreational drinking, as opposed to using it as an ingredient; alcohol is most certainly a food, and is used to flavor and pair with many dishes (not just in the cases where the alcohol is burned off, as with bourbon balls, but also as wine served with a meal) without the intention of achieving an inebriated state. Alcohol is made from fermenting a starch (wine from grapes/other fruits, whiskey from corn, vodka from potatoes, rum from sugarcane, etc.) Other fermented foods include vinegar (some vinegar is made from wine!), anything pickled, kimchi, and natto.
This again is misinformed; water consumed in high quantities will kill you, eating anything in a car can cause you to crash if you're not careful and anyone who blames alcohol for dancing topless on a table is lying to you, or themselves: alcohol does NOT change you as a person, though it may lower your inhibitions. A girl who's flirty/ does risque stuff when she drinks isn't doing it just because she's drinking, she was likely just too shy or embarassed to do those things before. A man who beats his wife when he's drunk isn't beating her because he's drunk, he's beating her because he's a wife beater. It's not the alcohol-- alcohol may exaggerate something about a person, whether its an emotion or their social skills, but it will not just flip a magic booze switch.
I drink for fun sometimes, but not often. I tend to get loud, silly, and very sleepy. The sleepiness is because alcohol is very much a poison, if a fun one, and it takes a lot of effort on the part of your liver to keep you from becoming poisoned by it. I already get loud and silly when I'm with friends, drinking just exaggerates it because I'm less concerned with being annoying and more concerned with maintaining my balance.
Someone in my immediate family is a "functioning alcoholic," which means while he drinks more than a normal person would or should he does maintain his obligations and responsibilities. His drinking is mostly related to self medicating, both for psychological reasons and having a bad back. When he drinks he talks louder, tends to write longwinded facebook posts, and sleeps. (I would go as far as to say that he has trouble sleeping if he is sober.) Sober he is very shy and self contained; any time he has to be social he drinks. Because of him I only drink with my friends, never alone. I worry that I could also become an alcoholic due to being related and having similar issues.
Alcohol is often treated as an excuse for poor behavior, but it's not one. It's very important to know your limits, and to know that if you may do something you'll regret, such as "dancing topless on a table," that you don't drink, or are accompanied by friends who will reel you in and get you home before you do.
Overall your idea that alcohol would ever make you do something out of character or something you would Never Ever Do is a misconception, and following that idea in writing would perpetuate that particular myth, so please do not. It can make your judgements worse, but it doesn't change the actual person. Whereas someone would be too scared to do karaoke sober, they may be the most enthusiastic karaoke singer ever drunk-- the want to sing was always there, the alcohol did not create it, it just made the person less scared of what other people would think.
The only case that alcohol could "make someone do something they never would" is in the case of sexual assault, because an inebriated person can never consent to sex, not even of both parties are drunk.