Besides social situations and stress here are a bunch of other things that may trigger blushing for some people.

Coffee
Caffeine-containing drinks such as strong coffee and lots of cups of tea can stimulate the body's natural sweating mechanism and blushing. Heat and caffeine make you blush a lot easier. If you need caffeine I found Red Bull to be the best. Lack of sleep my put you in a calm mood, but this is very individual, some people blusher more.

Alcohol
May worsen FB. Different liquors may contain different amounts of histamine that I believe is the reason for this. The break down of alcohol in the body actually puts histamine breakdown on hold, meaning that any histamine consumed in the body will have a greater effect than usual. So even if histamine is not normally a problem it might be when you drink.

Shaving (In the face)
Don’t shave in the morning instead do it before you go to bed. Shaving may cause skin irritation and your skin may feel hot, and this feeling alone can trigger a blush attack.

Flushing caused by drugs
A few drugs can cause flushing, so it is worth checking whether you are taking any of the following:

Chlorpropamide (for diabetes), which can cause flushing if you take it with alcohol
Diabinese (for diabetics) and niacin (for lowering cholesterol, sometimes contained in high-potency vitamins)
Glyceryl Trinitrate, Isosorbide Dinitrate (for angina)
Tamoxifen (for breast cancer and some other conditions)
Buserelin, Goserelin, Luprorelin and Triptorelin (for prostate tumors in men)
Raloxifene (for osteoporosis)
Calcitonin (for some bone disorders)
Calcium-Channel-Blockers (for angina or high blood pressure).
Morphine can cause flushing due to histamine release.

Viagra - Used for impotence or by guys that wants to be a stallion for a night. =)

Niacin - (for high cholesterol) Niacin may cause flushes. Niacin is also known as Vitamin B3 or Niacinamide. It is heat stable and water soluble. It was first discovered when scientists were looking for the cause of pellagra. It is absorbed in the small intestine and excreted in the urine. The human body uses niacin in more than 50 chemical reactions. It is needed by the body to extract energy from fat, carbohydrate and protein. It is a natural cholesterol regulator, and often works as well as prescription medications for persons with mild cholesterol problems. This formula uses nicotinic acid, the form of niacin that has shown promise in lowering LDL levels of cholesterol. Like all members of the B family, niacin plays a role in energy metabolism. Niacin has the property of causing the small blood vessels to increase in size. These are the capillaries.  Now, capillaries are often so small that the blood cells pass through them in single file. It is the capillaries that take care of the vast majority of all the cells in the body. You have large arteries near the heart, and they get smaller and smaller as they extend from the heart.  But, at the end of every well-sized artery is a very large network of capillaries. They all start from the heart -- but at the end of the line they are tiny, tiny capillaries