pay off the principal
Not to be confused with the shrewdly-prudent and virtuously-responsible practice of
diligently settling your bills "up front and in full" and therefore carrying a zero balance (i.e., your "principle") on your credit card each month to avoid interest-fees, this term refers to the decidedly
UNWISE and UNFAIR act of BRIBING (i.e., "paying off") the head-honcho at an establishment of learning (i.e., the "principal"), so that he'll kiss-buttingly bow to your outrageous stipulations and/or preferentially pull strings on your behalf, often to the detriment of others in the school.