There may well be some confirmation bias going on here and my sample isn't exactly clean, but: have you ever noticed that, of the people you hear speaking more loudly than would be considered socially appropriate in a public place, a dispropotionally large number of them aren't speaking english?

I have wondered about the psychological reasons behind this. I think that maybe this is so because people who are speaking a non-native language are used to people not being able to understand them and thus, being largely ignored by the rest of those present. They've probably seldom been asked to be more quiet because people hearing them may suspect/assume (perhaps subconsciously) that they cannot understand english and so would not comprehend the request. Speaking a language not understood by the majority also mostly negates the need for to be quiet to keep one's topic from becoming known to those around and to keep others from butting into the conversation.

What's really funny (and annoying) is when you hear people nearby speaking very loudly in a foreign language and then, when the switch over to english, they get much more quiet, only to get loud again when they go back to whatever it is they were speaking before. I witnessed this the other day in Target. This behavior indicates that they are, in fact, conscious of the fact that there are people around them, but they just don't care - using the fact that most people don't know what they're saying to keep their conversation private without having to bother with being courteous.

Just because i don't know what you're saying doesn't mean i can't hear you.

~PS