Probably the biggest one I can immediately think of is for a man to sit alone in the back seat of the taxi.
Probably more common in other countries with a peculiarity to try and rip you off or imprison you in the back. Makes it easier to ditch the taxi if things go pear shaped.
You've obviously never caught a Melbourne taxi, I can't remember the last time I had a taxi driver who could speak English well enough for any sort of conversation!
Very harsh guys! Not only do I catch Melbourne Cabs (MEL is home) but I actually catch Dandenong cabs! I find it's all about giving them a chance, yeah they may not have an awesome grasp on English but they've got some great stories.
I care more about their ability to get me to where I want to go effectively. Taxi service first, stories second.
Maybe I don't have a large enough sample size, but so far in Melbourne as far as knowledge of how to get to where, it has to be
the worst of the taxi drivers in this country. Speaks to be more embarrassing when over 95% of them have a GPS (but surely a good taxi driver should be able to drive to at least 80% of a city without needing a GPS perhaps until they get closer to the destination).
The left hand being offensive in Muslim countries is probably one that many will stuff up, especially if you're left-handed. Pretty much gesturing with the hands, one needs to be always careful of the local custom.
"Don't speak the language if you don't know how." A bit of a blunt and unfair statement; certainly doesn't do much for encouraging people to embrace languages and lingual diversity. (Yes I realise we have a double standard application in Western countries, but that's beyond the point). I know what it really means to say is if you are going to utter a few words in another language, make sure you know how to say it properly, as saying it incorrectly may offend (even if unintentionally).
People from other cultures are often heartened to hear even a few words from foreigners of their language, even if those are the only words they can speak and you quickly go back to speaking English (fluent or pidgin). It helps break the ice.