Speak to humans or elves unless absolutely necessary.
Answer questions of humans or elves--just stare for a moment.
Yield. On anything. Ever.
Leave the field without killing someone.
Orcs in combat will often break up into packs of two or three, each pack attacking a single opponent if possible. Orcs are strong and dextrous, and specially designed armor allows tumbling and rolling manuevers to quickly flank or escape an opponent. Orcs delight in combat and laugh while fighting, which disconcerts most opponents. War horns and drums also tend to create panic among their enemies. A General usually stands on a high place to one side of the battle, shouting commands in Orcish. The General will not actually join the fray until the unit's orders are given and undertaken.
Orcs are fiercely territorial, even the nomadic tribes. Encampments are usually guarded, and orcs sleep with their weapons within arms reach. Archers usually stand ready to pick off any intruders, bipedal or otherwise. While they don't grow their own crops, some tribes of orcs do raise a variety of cattle. They serve as beasts of burden and food, but orcs do not ride.
The typical dress of an orc is very loose. Kilts and tabards are fairly standard, as are loincloths and mantles in desert regions. Orcs in colder climates often wear a variety of hakimas. The coloration of most orcish dress is suitable for simple camoflauge appropriate for the environment. Orcs generally wear some form of armor at all times, and for special occasions they wear decorative ceremonial armor over their clothes.
Orcish religion is mainly ancestor-based. Orcish legend states that when the gods created Araudakog, the first Orc, they all fled in fear, having realized too late that they had created a being too powerful for them to control. Araudakog was possessed of the greatest gifts of all the gods. He was mighty and dextrous, cunning and tireless. He crafted a weapon of superior virtue, which to this day bears his name. Taking up his beargutter, he hunted the gods down one by one and slew them and ate their beating hearts, delighting in the taste of their blood. To this day, orcs revere the heroes of their race and often attribute to them the slaughter of various supernatural beings.
While orcs are generally characterized as evil, it would be more accurate to describe them merely as aggressive. They do not care for the company of elves because elves are renowned for their delicacy and physical weakness. They will, however, fight alongside the hardiest men and view them as near equals. However, Orcs respect only power and will follow a strong leader as long as he shows no weakness. Always eager for battle, orcs will ally themselves with a larger fighting force if the spoils are good and the leader is very strong. The strength of the army is usually tested at an orcish banquet where games of strength and skill display one's prowess, and powerful drink tests one's internal mettle.
Orcs don't ask.
Let not the sun rise on a clean weapon.
A scar is a tale told for you.