you say it when you remember that Zach is cool
if you dont capitalise the word "Zach" it is considered to be a racial slur.
# example 1
person 1: DUDE I JUST REALISED Zach is cool
person 2: Dude Zach is cool
# example 2
person 1: DUDE I JUST REALISED zach is cool
person 2: Dude kill yourself