The Stereotypical Thai Gender Roles
In every culture there are stereotypes for guys (poo3 chai 1 ผู้ชาย) and stereotypes for girls (poo3 ying5 ผู้หญิง). Boys like blue, girls like pink. Boys like action figures, girls like Barbies. It is of course only a stereotype, i.e. what the culture assumes and accepts as the truth - whether it is or not.
It's no different in Thailand.
Now before I start describing these Thai stereotypes of gender, keep in mind that culture changes over time. As such, stereotypes are different for different generations.
Stereotypes for Guys
1) Most Thai guys drink a lot, and often. (deum1 lao3 boi2 ดืมเหล้าบ่อย)
This stereotype is generally true for a good majority of Thai men. They like to drink when they go out to socialize. Heavy social drinkers, you can say.
2) Most Thai guys smoke. (suub2 bu2ree2 สูบบุหรี่)
This stereotype is definitely not as true as their drinking habits, but a decent amount do smoke. Based on the highly scientific study that I just made up today, I'd say 30%+ smoke socially.
Interestingly, if you tell Thais you don't smoke or drink, they'll be approving/surprised/impressed. They'll still smoke/drink, but they'll consider you a good person that you don't.
3) Most Thai guys cheat on their girls. (poo3 chai1 jao3 chuu4 ผู้ชายเจ้าชู้)
To be honest, this stereotype is really hard to verify. But from my experience in Thailand, I often see evidence that reinforces this stereotype. It's not unusual that a Thai man would have a second or third wife (meya1 noi4 เมียน้อย), if he could financially support them. What isn't so fair to Thai men is that Thai women want to be with men who are already married, meaning they are equally to blame. And from my experiences in Thailand, they also cheat just as much as men do. However, the stereotype for women is that they don't cheat - it rarely even crosses anyone's mind that it happens.
Stereotypes for Women
1) Women like to dress up, be girly, have fancy clothes, and expensive purses. ผู้หญิงชอบแต่งสวยๆชอบของแพงๆ
This is no different from western culture, so no further explanation is required =P
2) There is no such thing as a woman who isn't 'Noi Jai' on a daily basis.
There is no word for noi4 jai1 น้อยใจ in English. It's when a girl is annoyed with her man, so she gets pouty, sarcastic, quite, or has an angry outburst because of some perceived problem she has with him. Have you ever had your girl act angry at you but you didn't know why? That's called 'noi jai', her state of mind in that situation.
This music video has a lot of noi jai examples. Not my style of music, but you can generally figure out what's going on . . .
3) A good girl is never alone with a man. A bad girl has tattoos.
This is one of the older stereotypes that's changing, so some strongly believe this and some don't. Some Thai women, if you ask them out on a date, they'll bring several friends with them on the date. From the western point of view this can be extremely confusing, no? It's considered inappropriate (mai3 maw1 som5 ไม่เหมาะสม) to be alone together. It's still common to look down on women who go to bars and have tattoos. Fortunately, although unlike in the past, it's no longer assumed that Thai women seen with foreign men are prostitutes.