Loud people in all their varied forms.
The basic antisocial sort who think it's fine to broadcast their music to the entire bus/train carriage on the tinny phone speaker.
The drunk folks getting out of the taxi at 1 in the morning. I'm not even talking about fighting or loud arguments, it's the slamming car doors and laughing too loudly. FFS there are people asleep... or trying to.
Barbecues. People who seem to think it's their god-given right to get the loudest possible speaker going. And laugh at 200 dB!
Just shut the hell up and be quiet!
I'm not sure which type is worse. Those who are genuinely unaware of their effect on other people, or those who are aware but think they are more important than anybody else.
The above applies to adults who should have developed some basic awareness by now. I don't mind young kids letting off steam, they get a pass.