When using chopsticks, one must never stick them in ones bowl or food upright, so that it is perpendicular to the table. This is considered extremely disrespectful.
I was born in China and imimigrated to the United States with my family when I was in second grade. Ive been living in the states ever since and while I am American in many aspects, I still retain many traditions and cultural ties which makes me uniquely Chinese-American.
As is true with most Asian cultures, respect, honor and saving of face is closely associated with etiquette. There are etiquettes for almost everything, a proper way to do this and that and table manners are no exception. One particular table blasphemy I remember from childhood concerns chopstick placement.
Theres a reason why when one walks into chinese restaurants chopsticks are laid flat on the table. In the case of more upscale Chinese dining, there are even chopstick stands where one can place their chopsticks so that the tips are slightly elevated from the table. It is considered disrespectful and wrong to stick chopsticks upright in ones food or rice because this resembles what people would do with incense in front of graves to honor the dead.
Many Asian cultures burn incense at temples as a way to pay respect to the Gods. It is also used to honor the dead. Usually, one would take a burning incense between both palms, bow three times in front of whatever entity, be it a god or the recently deceased, then place the incense upright in a soft mount in front of either a temple, or a grave. Because the notion of sticking chopsticks upright in a ricebowl is so much like the incense procedure, that is why it is frowned upon. In fact, Ive also heard of cases where people would literally stick chopsticks upright in food to leave food for the dead, so that the spirit can come back and use the chopsticks to eat.
Besides being disrespectful, since its almost like playing with food in western cultures, it is outright bad in the sense that it is morbid and associated with death. Especially if ones dinner host is superstitious, it is best not to do anything crazy with ones chopsticks.