Question

Why did Snape tell Harry Potter that he was the Half-Blood Prince?

Answer 1

Maybe because harry had took the one book in professor,slughorns class and harry found the name "half blood prince" and hermione reported it and snape found out.

Answer 2

because he wanted to tell potter to back off. "you dare use MY OWN spells against me?!?!?! Yes, Potter, for I AM THE HALF-BLOOD PRINCE!!

Step-by-step explanation:

snape knew ever since the draco in the bathroom insident (snape came up with that spell) so he just wanted harry to know that it was because of him that his potions grades were amazing.' it was me who came up with that spell that you nearly killed draco with.' it was pretty much another giant ____ YOU to harry.