Just Say No
Back in the 80s when Nancy Reagan came out with that "Just Say No" campaign, people laughed and lampooned the idea that all it takes is a "no".
But even now pop pscychology will tell you to simply say "No, I cannot.", "No thank you.", and "No, I am not available." in a clear, firm voice. Just say no and do not offer any explanations or excuses, they say. People will respect that, they say.
Just who are these people exactly? Sure, if you say no to a free newspaper as you are coming out of the subway, someone may respect that.
But if it is someone with whom you have a more than slight acquaintance, they are not having it. I am sure I have done my fair share of cajoling myself.
A "no" is usually followed by reasonings, accusations, and all-expense-paid guilt trips.
So if I have told you no recently, then yes this is for you.
Rinse. Lather. Repeat.