You're a Sydney-sider and you were on the train at 1:20 and one of the people in question was a 14 year old male, this didn't happen to the 443 going to Bankstown right? I kid, I kid.
But in all seriousness I feel a bit wary about posting here, oh I've got stories about peoples conversations ticking me off but occasionally (it's pretty rare though) I'll be on a public bus heading home at the end of a schoolday but due to the bus schedule it'll be the same bus as a couple of mates, we sit up the back but damned if our conversations aren't sticking out against the silence (but it's normally just jokes about videogames and other mostly harmless things).
From a non-guilty standpoint the worst kind is phone conversations, at least when all the members of the chat are within a close proximity you get a sense of structure. Some of the worst contenders I've had are when I'd be watching some tv with my sister then she'd get a ring and hold the conversation for the entire program, or this one time when I was in an airport bathroom some bloke sitting in a stall was getting furious in a phone conversation which I can only assume was with his wife. I think I had a pretty big lot to dump so to speak so I heard the whole thing but the guy was so scary in his wrath that I think he helped speed it up a bit, eff this and eff that, you effing w**re, effing listen to me. At then end of it he said (and I quote, though some parts may have been slightly edited to protect the souls of all short children and big babies on this fine forum today) "I am sorry to all those who had to hear that but women, if they didn't have c**ts then they'd all be stockpiled in a warehouse". Mind you on the bus of an afternoon I have a plentiful plethora of conversations to listen to, though my choices are usually limited to cliched girls talking about parties and even what they...do with their partners (which is funny because they're normally younger than me) and cliched boys talking about manly things like "Cod" and probably other varieties of British fish.