Travelling around Southeast Asia will more than likely give you a huge culture shock if you're used to Western culture. Its a place where pretty much anything goes and you need to learn to expect the unexpected. My first time in Asia was in the Philippines and in fairness the difference wasn't so much as a shock to me as I had visited Marrakech the year before, which was without a doubt the biggest culture shock I've ever had, but there was still so much I couldn't get my head around.
The main one that I think shocks a lot of people is the roads. Arriving in a new country and having to deal with the chaos that is Asian driving is insane, especially coming from somewhere like England! There seems to be no rules on the road whatsoever. Lanes, traffic lights, pedestrian crossings don't seem to mean anything and people pretty much do as they please. In Ho Chi Minh, where I've just visited, the only way to cross is to simply walk out into the traffic and hope for the best. They have around 11,000 deaths a year from road accidents and yet you will still find crazy driving including fitting families of five or all manner of objects onto their motorbikes.
There are a few other things I struggle with while I'm away including odd translations. For example whilst in an airport a few weeks ago I ordered what was described to be vegetable spring rolls which in fact turned out to include pork and shrimp. The waitress could not understand why I hadn't expected it and as I do not eat meat it was a pretty big deal for me. Of course I understand English being someone's second language mean the translations aren't always perfect but sometimes even the simplest of translations are way off!
Another huge difference I noticed whilst in Bali is the difference in how countries are led or policed. Coming from England we are used to laws and regulations but in other countries their legal systems can be a little different. For example in a taxi in Bali the driver drove the wrong way down a one way street and after seeing the police he groaned about having to pay him off so that he would not get into trouble. We also heard a number of stories from other tourists who were stopped by police when on motorbikes and asked to provide their licenses. As licenses are, for some reason, not something that is required to rent a bike not many people have them on them. The police know this so the tourists are then forced to also pay a fine in order to avoid getting in to trouble.
As much as the differences in cultures can be a little surprising or even unerving at times I love the feeling of going somewhere totally different to home. I like to see how the locals really live and enjoy learning about new cultures and traditions. I also love to try the local food (although I'm limited to the vegetarian options) and try to push myself out of my comfort zone. Travelling teaches you so much and I think an understanding and acceptance of other cultures is one of those. Keeping an open mind to the craziness and expecting the unexpected makes it a whole lot easier to get used to and my advice to anyone who may be experiencing their first time in Asia is to just go with it and enjoy being somewhere so totally different.