Why are some people mean or annoying drunks?

[sunshinexoxo1]

Meanwhile my personality remains the same even if hammered; it only goes from happy to very happy and slightly more friendly, some people changed completely. Why?

Even with a strong drink, people still tell me I'm the same, just more laughter during conversations but nothing else.

[MrOracle]

When you drink alcohol, the first thing you lose is your inhibitions, and the second thing you lose is your judgement. But beyond that, different people are effected differently by alcohol. Some get "happy" and silly. Some get sleepy. Some get sappy and tell you they love you 500 times. Some get angry. Some get violent. And while often this is just an amplification of their baser selves, there are a few people who are reasonably nice, non-violent people when sober who get violent and angry when drunk, like they're a completely different person. And you can't always predict who that will be.

This is why bars and clubs pay for bouncers. It's such a common problem that they have big guys who will get such people out of the space as quickly as possible, and prevent them from coming back in where they're more likely to harm the business.

[Quogha]

Alcohol affects everyone differently. Some people become annoying. Some people become violent. I avoid bars, clubs, and parties for this reason.

I drink socially as well, occasionally more than I should. I avoid inviting anyone who becomes annoying, violent, or excessively drunk. I’m lucky I know almost nobody who does though. The people I hang around all have a similar demeanour. Laughing, relaxed, and having a good time.

[Fireguy17]

EtOH tends to enhanse a person's personality.
If they are an ass hat before they drink, then they are just a bigger ass hat while drinking/drunk, same goes for someone who is funny etc, for the most part.