Dear You,
Every time we meet, you ask for my help; from carrying a package, to delivering a message, to giving you a ride, to paying your rent. But when have you ever been willing to help me? Every time I ask for your help, you don't have the time, or you're tired, or you're not feeling well, or you have to meet a friend, or anything to keep you from returning any of those 'favors' and 'loans' you keep asking for.
I just wanted to know that before I stop saying 'yes' to your requests, I am going to tell every one of our mutual acquaintances exactly what kind of person you are - a financial and social deadbeat. Then I will cut you off. From that point on, I am no longer doing any 'favors' for you. If you ask why, I will remind you that you still owe me the money I loaned you from last year. Not that it is going to break me financially, but that it might finally give you an inkling of why everyone else is going to be turning you away as well.
Come to think of it, I seem to be the only person you come to when you need a 'favor' - could it be that they already know? Do you already know that they know? Honestly, I hate being unaware of exploitation almost as much as the exploitation itself.
Ah well, live and learn ...