In the 1960s–70s, there was a popular (though unscientific) medical fad in China where people would inject chicken blood into patients, believing it could cure various illnesses and boost vitality.
Of course, it didn't really work, but the association of "chicken blood = sudden energy boost" stuck in the language.
Modern Slang Meaning
Now, "full of chicken blood" (打了鸡血 / dǎ le jī xuè) means: Overly excited, pumped up, hyperactive, or fanatically motivated.
Think of someone acting like they just got a sudden injection of raw energy.
Examples:
"He's acting like he's on chicken blood today, can't sit still for a second."
"That fanbase went crazy, it's like they were injected with chicken blood."
In Web Novels / Pop Culture
You'll often see phrases like:
"He went all chicken blood in battle" → suddenly fought like a man possessed.
"The crowd was full of chicken blood" → everyone was ridiculously hyped, way over the top.
It's often exaggerated and humorous, implying someone's enthusiasm is too much, almost irrational.