There are times when I'm being used without knowing it. People always take opportunities at the right time and situation. It is not a sign of vulnerability, but maybe weakness. I hate myself being put into a situation when "NO" is not an acceptable answer, or even the answer that people wanted to hear. When actually "YES" is being heard close to 90% all the time, the remaining 10% are usually the one from my own decision e.g. product promotion, bank loans promotion, insurance promotion, telco promotion, and etc. Some of the situation where "NO" is probably not a good answer is...
... when your close friend wanted to borrow your money, but he still owed you the previous one
... when someone used a person's name & position to "black-mail" you in completing a job last minute (and in short time)
... when somebody try to get an info, but knowing that the same info is available somewhere else and the other guy is clueless on how to get it
... when a task is being assigned from someone else (either permanent or temporary) without proper handing-over, and is expected to deliver the same quality as the previous
... when you are being given a very important job at the eleventh hour, but at the same time you have your plans for the weekday or weekend or holiday
there's a lot more, but I'm having writer's block due to heat...