You'll find elders who tell you not to point at the rainbow or you will lose a finger. This becomes interesting because the Nak are connected to rainbows, per myth, so I wonder if there's a connection there. There seems to be a growing belief that if you eat snake by the Mekong, you inviting death, particularly by "drowning." Most likely you offended a Nak, who would also be inclined to do you in if you're partying and frolicking in their clean and tranquil waters.
But let's get to the good stuff. There are numerous superstitions connected to phi and other denizens of the spirit realm, especially at night. Here are a few that people have discussed.
If you see your child is talking to someone who isn't there, you should set food out and show respect if you know what's good for you.