@skpotamus: Thanks for posting the links to the vids. Two things, though: Firstly, you're right, I don't wear jeans like that, the jeans I usually wear (and which most people my age wear around London, to be honest), while not being "around the thighs" seriously restrict how high you can kick. As I said, about the hip is as high as you're likely to go, and even then, you'll be fighting against the jeans. I was very impressed by those videos, I've honestly never seen jeans like that. Also, I wouldn't be caught dead in a suit as baggy and horribly cut as the one in the second video you linked.
Secondly, I'm glad the clinch works out for you in street fights. I still don't recommend it. You ask why people would follow ring rules in a street fight: they follow ring rules because they've been training ring rules for years. Not many proper Muay Thai gyms teach students how to knee people in the groin during a clinch, and almost no Nak Muay who's training for a bout bothers to drill kneeing to the groin, or defend a knee to the groin. Because it's just not part of the sport, it doesn't get taught, and it doesn't get trained.
I'm not saying that a Nak Muay will out of principle refuse to knee someone in the groin, I'm saying that if you've trained the clinch for 5 years with (almost) complete confidence that you can go into clinch without getting kneed in the nuts, you will by definition not be as ready for a knee to the nuts as you will be for say, a hook to the face, or a kick to the stomach, which you most definitely WILL have drilled in the gym.
My advice is to stick to ranges where you know (and control) the game. If you're both unarmed, stick to punching and kicking ranges, because there's absolutely nothing Muay Thai can't handle at those ranges. In grappling range, you're dealing with joint locks, chokes, groin strikes, biting, and eye gouging, all weapons you haven't trained to defend against.
And forget about it if he gets you on the ground and you haven't done any BJJ. I'm not saying he'll definitely beat you at these ranges, but you're throwing away the advantages your training gives you if you let him get to these ranges.
That's my two cents, anyways.