Harry Gracey used the term boot camp to describe kindergarten.
Harry Potter is set in Britain not America. Kindergarten is something in America not Britain. The equivalent would be nursery and the name of it is unknown.
In Harry Potter, a kenning is a poetic phrase to describe magical creatures or objects. For example, "He Who Shall Not Be Named" is a kenning for Lord Voldemort. It adds an element of mystery and magic to the storytelling.
The phrase "supermegafoxyawesomehot" is used by Harry in Act 1 Scene 6 of A Very Potter Musical to describe Cho Chang.
He is the protagonist
The closest you can get to a Catch Phrase in Harry Potter would be the classic "Bloody Hell"
Hes got lots
"At the end of the day."
wieners
folk tales
I am not aware of Harry Potter repeating a certain word or phrase regularly.
Probably the spell 'Expelliarmus', as Voldemort locates Harry for using that spell.
Harry Styles.