My one from this morning:
"No Mr Smith, you are not the best thing since sliced bread. I have actually put in the work and achieved professional exams, starting my own business, and being happy with my life, unlike you who just seems to talk a lot about achieving things without actually getting up and doing anything. Your life coaching business is a fraud where you rely on cash-rich clients knowing even less than you do. Now pay my invoice and don't come back until next year."