Probably the time I took money off of a homeless man. He came up to me in the street and asked me for money, I thought "why not do a good deed for the day" so I gave him a pound coin. He thanked me and walked away.
But as he was walking away, it dawned on me that I may have just been swindled by a con artist. What if he wasn't even homeless and I'd just been taken for a mug? How dare this gyppo cunt manipulate me into giving him money? I was furious. I got really mad so I decided I'd con him back. I ran after him and pretended that I just realised I needed the money for my bus fare and asked for the pound back, he apologised and gave it back to me.
The thing is, after he gave the pound back he looked all remorseful and was all like "I'm sorry I might have caused you to miss your bus, take care" and then he hugged me, so in all likelihood he probably wasn't a con artist and was actually homeless after all. Oops.