姑娘百毒不侵少年无情无义
[gū niáng băi dú bù qīn shăo nián wú qíng wú yì]
The name 'A girl immune to all poisons and a heartless boy' implies someone who believes that she (the girl) has become resistant to emotional hurt (poison), while the boy (man) does not feel emotions or act kindly. This often signifies someone with toughened-up hearts, especially after experiences that left them emotionally numb or hardened.