On Guani is a phrase that is a way of saying that someone is
telling the truth. Similar to other phrases such as "I
swear to God." Other common uses are "On my mom," "On
my grandma," "On my grandpa," "On gang," etc...
Person 1: I whipped out of that
parking lot so fast,
spinning the wheel, I 'bout flipped the damn car over. Then
the police started following me, and I had to run away.
Person 2: Really?
Person 1: On Guani