I'm not sure why all the backlash at the OP. Maybe there was a better way to say it but this is a concept surely everyone can relate to. People are LOUD and sometimes that's really annoying.
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Come on! I am a patient person. I live in a very busy urban area. I am content to hear a lot of noise but sometimes people are really goddman inconsiderate. If you're telling me you've never had a day of feeling irritated by people noise, you're either living in a desolate place or lying.
You said it exactly as I feel it, every day on public transport. For some reason it's much worse in the afternoon, when people are going home for the day. I suppose they're too tired in the morning.
I don't mind discreet phone calls. We live in an age when people are expected to be available a lot of the time, and sometimes you really have to give or get a message. IMO it's possible to make or take a short call in a way that's respectful to the people right next to you.
What drives me crazy is when someone SHOUTS into the phone, and is clearly just chatting away because s/he's bored. It's really, really hard to tune out someone shouting their personal business 1 meter away from you. A few times I've gotten a serial-telephoner right next to me. It's always a female. These people spend the entire trip calling one person after another, just to chat, and they SHOUT into the phone.
If I were to ask these people to please keep it down, I would be doing it Every. Single. Trip. I'm not overly sensitive, I really think it's just the attitude here. Common courtesy is not something you see a lot in public.