There are many articles in books, magazines and online about the value the Thai put on "face" and how important it is not to "lose face" - and one of the easiest ways to do so is to let your emotions get the better of you and lose your cool. It's not just uncouth, it shows a weakness of character and a decidedly UN-Buddhist way of dealing with people who are well over 90% Theravada. It's extremely bad manners and not soon forgotten by the Thai you deal with. It rolls out the welcome mat for bad karma, too.
For example: you make an appointment with someone to meet you for something tomorrow afternoon but you lose your temper before parting that day. They may not let on you've committed this social sin, but they also may not show up for that appointment; avoiding the confrontation, but choosing not to deal with you further.
The problem with that for me is that I tend to have an easier time slipping into my cranky pants if I'm (a) frustrated (b) physically uncomfortable or (c) not rested or feeling well. I don't know about you, but put me into a humid, tropical area fifteen time zones removed from my home with a culture that can seem completely upside down from my "norm" and it's far too easy for me to be dealing with all three of those hot buttons at least once a day. Usually I can count to 10, take some deep breaths and practice what I've heard called restraint of tongue and pen.
My closest friend in Thailand thankfully is now able to joke about the afternoon we were walking in downtown Bangkok and trying to make our conversation heard over the razzing din of a large group of tuk tuks, swarming past us for what seemed like 15 minutes. Pausing mid-sentence, I turned toward the street and angrily screamed "SHUT UP!" at the traffic. Knowing it was a completely futile gesture I thought I might slide it by as silliness, but my friend stopped dead in his tracks.
His face gone sober he avoided my eyes, staring for a few seconds at the sidewalk in front of him before beginning to walk along again. I tried again to pass it off as a joke, but he looked directly at me and said "Why you shout? Not good. Not jai yen. Jai yen yen."
Jai yen yen means "calm down" in Thai, as in "please calm down" - something I knew by his tone of voice without even having to ask. All three of the above buttons had been pushed repeatedly that day and unfortunately I'd finally given in to them. It was out of character for me, and I'd genuinely shocked him. I apologized profusely and did what damage control I could by explaining why I'd lost control as we walked along, and soon he understood, allowing that he's had days like I'd had, also - and had also lost his temper.
The commonality of it allowed us to get past it, to the point that he also did some cartoon-like mock shouting later that evening: at the BTS train we'd just missed, at the television - giving me a sly sideways glance each time he did it, as a reminder of how ridiculous I looked shouting at the traffic. It's become a running joke for the last few years, and either of us is liable to fake rage and pantomime "shouting" when things aren't going as we'd planned or wanted them to go.
I was lucky that time, and have made a sincere effort to keep my cool heart there since.
[There's a follow-up example to this post on December 2nd of this year, if you're interested.]