To understand "public display of affection," we need to know about the internet slang "单身狗" (single). To be specific, "单身" in Chinese means "single" and "狗" means "dog." Normally, only a person would call himself or herself "单身狗" in a self-deprecating manner. When a couple becomes touchy-feely in front of singles, this is called "sprinkle dog food."