One thing that irritated me was the fact that the Thai character, Noi walks around her house with her shoes on. I'll admit that I have never been to Thailand, but it is undisputed that removing shoes at the door is a universal norm in Thailand, apart from some of the highland tribes (I believe). I suppose that there might be a few odd Thai people who don't take their shoes off, but this would be so unusual in Thailand that it would be worthy of comment in the film.
I thought about a number of reasons why they had a Thai character breaking this fundamental rule of Thai behaviour. Perhaps the film is following the habit of American films of never having characters take their shoes off at the door. This would make sense if the film was keen to attract a western audience.
The fact the Thai character wears shoes in her house does build up the contrast between her slovenly and chaotic ways and the fastidious and obsessive-compulsive Japanese character. I'm not sure this was realistic though. I imagine even a slob in Thailand would remove his or her shoes, perhaps not for cleanliness, but just out of habit.
Another reason might be that the director wanted to make the moments when the character was barefoot seem more sexy and cute. The sexiness of her being barefoot might be reduced if she was barefoot for most of the film. I recently watched the Japanese classic, Tokyo Story (a beautiful film). As a result of its domestic setting, a lot of characters are barefoot for much of the film. I can imagine even a foot fetishist losing interest in all the female feet on display in that movie. In Tokyo Story, being barefoot is part of the mundane domestic reality of Japanese family life, where in Last Life in the Universe, being barefoot is meant to be cute and sexy.
The disregard of Thai norms with regard to shoes brings up some of the problems I had with the film. I don't think I learned anything about Thai culture from it. Noi, the female character could just as easily have been French or South American. The film could have been set in any country where there are a lot of Japanese expatriates living. The absence of any real exploration of Thai culture is magnified by the fact that the director decided to have the Thai anthem played rather pointlessly in one part of the film. More so than this, it seemed that the two characters existed independently of any society at all. I understand that the film is all about loneliness and isolation, but it seemed like it was following that dreadful habit of western romances of creating characters who are unbelievable because of their lack of wider social interaction. In so many romance films you have characters who are never seen to be working and don't seem to have any worry about paying bills. The protagonists of Last Life in the Universe seem very close to that category.