What does it mean to say your blood is boiling ?

It means that you are ANGRY. 
"Seeing red" is another expression for being angry.

It means you're fuming- (really mad). Some folk say stuff "makes their piss boil" as well. 

That you're so angry you've got steam coming out your ears. 

It mean, the temperature of your blood is above 100 degrees celsius, the boiling point.

When anger becomes unwantedly powerful in dominating reasons, mental stability, then a person can be said that his blood is boiling.The repercussions of blood-boiling in this case are apparently dangerous.

Very angry. To the point where your temperature may actually rise. And blood pressure rises 

This is another way of saying that a person is extremely angry.

It means that you are very angry 

Blood is boiling means to cause someone to be very angry.

It simply means that 'your about to loose your rag'.

It means that you are VERY ANGRY.

Boiling with ANGER