That at Chinese weddings the bride/groom give you money in a red envelope if you are younger than them and unmarried (and tenuously related to them by being the boyfriend of their cousin.)
Another thing I learned is that I am damn glad I'm not Chinese. Not only do you have to do the above, you are then expected to give much more money to people who get married down the line.
I learned Chinese people can EAT. A hog roast for lunch and a private rented ice cream van after the wedding service and then a 12 course meal in the evening.
But most importantly I learned that I am not entirely unable to control myself. An incredible amount of alcohol was offered to me and often entire bottles of wine were just plonked down in front of me, but I was able to stay sober. Coming up six weeks now!