An irritated or inflamed anal area. "The chappies" is a condition somewhat like hemorrhoids but on a more temporary basis. Chappies are usually caused by excessive ass wiping due to having the shits or by excessive moist farts causing a sore, irritated anal region.
"Damn, Frank's food was so greasy I had the shits all day. Now I've got the chappies so bad I can hardly sit down!"