含 (hán): To hold in the mouth; to contain or cherish.
血 (xuè): Blood.
喷 (pēn): To spray, to spurt, to gush.
人 (rén): Person or people.
The characters combine to create a brutally graphic image: holding a vile substance (blood) in one's mouth and forcefully spraying it onto another person. Metaphorically, the “blood” represents fabricated, ugly lies, and the “spraying” is the malicious act of public accusation.
This idiom is used in serious situations where someone feels they are being unfairly and viciously attacked. It's a strong, emotionally charged term.
In Arguments: You will hear it in heated personal or professional disputes when one party wants to accuse the other of fabricating lies to gain an advantage. “你这是含血喷人!” (“You're just slandering me!”).
In Media and Politics: News articles and commentators use it to describe political opponents making baseless accusations or media outlets publishing fake, defamatory news.
On Social Media: In online “flame wars,” users might deploy this term to accuse others of spreading malicious rumors or twisting facts to attack them.
The connotation is always intensely negative. It is a formal accusation of severe misconduct and is never used lightly or humorously.