A phonetic mispronunciation of "yīnyáng," or "yin-yang," which is a concept associated with the religious tradition of Taoism and the apparent dichotomies in nature (day/night, male/female, etc.) in association with traditional Chinese medicine.
Use of "ying yang," or "ying-yang," has seemingly allowed the word to take on a kind of "sing-songy" resonance with the additional "ng" sound placed on the end of "yin."
For many, it has become second nature to say "ying yang" instead of "yin yang" because of familial or cultural influences, such as family, friends, and teachers. This may stem from simple ignorance, within certain groups, of Taoism (pronounced Daoism) and other Eastern traditions.
Susie: Hey, I sure like that ying yang tattoo you got there!