We all laughed and teased him when his efforts in Vietnamese were greeted with (by order of frequency) incomprehending stares, polite smiles (followed by some action which was not what he asked for), and even, sometimes, loud guffaws from the rudest of his interlocutors.
Most recently, his tries were limited to ordering more drinks [Em à, dem thêm mot loon Seven Up. Cam on!] or asking for the bill [Tinh tiên!]. The funniest is when he practised repeating a sentence for a while until satisfied that he got the tones right, and when the waitress finally appeared, he said the sentence with the wrong tones! Hilarity usually ensued.
As with all speakers of non-tonal languages, the ex has enormous difficulties with the tones in Vietnamese. As his teacher and his coach, I never understood how non-tonal speakers could not distinguish the tones and yet, when asked to hum a song, they do it perfectly, in the sense that they don’t simply make a monotonous drone, their voice follows various pitches according to the notes. And yet, they can’t hear the tones, they cannot distinguish among them when they hear them and even when they do recognize them, they cannot reproduce them.
It was all quite baffling to me, until I read an article in The Economist (May 31st, 2007 edition) that says that the speakers of tonal and non-tonal languages have genetic differences. It’s too complex a field to be explained correctly and succinctly in a blog (and by me, a recognizedly slow mind), so I will send you to two of the various sites that analyze the issue: http://tinyurl.com/2fz6x9 and http://tinyurl.com/2fwpeq.