Mine are always rubbish. My best one though is when I convinced a foreign friend of mine that there was also the cheese bunny, for people who were allergic to chocolate, such as Diabetic people. She didn't believe at first, but thanks to a poker faced Oscar winning performance she started to. Once I saw that giveaway look on the eyes of belief, hope, trust (she really likes cheese) etc then I couldn't handle it any longer and laughed my t*ts off.
I had a whole alternative reality going with history and everything. Good old Monks of Chedar used to hide from the money grabbing friars of Cadbury, and would hide their cheese loops in the... well, you get the idea...
Oh, and a friend of mine once called me up from a prison cell, and then came up with this long winded story of how the filth caught up with him, and he needed my helping hand. We all believed him because he was a complete scally, plus it sounded like he was in a police cell. Which he was just outside apparently. But he wasn't arrested. Oh, and we were very very drunk. It backfired on him though as we couldn't give a monkeys and left him to rot. This was mainly to get back at us for going out a lot without him, then phoning him up at 1am to say we are having a great laugh with a load of birds in the next town over to him. Which we were. Just not in the town we told him... and considering towns are like 20 miles apart where I come from, he wasn't best pleased. And several other times when we did the same thing, but claiming to be in accidents and needed help. And we thought Andrew (his best mate) was dead. Luckily I am an extremely good liar. Arf. You had to laugh. He didn't though, miserable git.
Cheers
I am 99% probably lying in bed right now... so don't blame me for crappy typing