The last Thursday before Halloween.
On this day, like April Fool's day, you just play a trick on someone.
The only thing is, you aren't allowed to tell them it's a trick till the next day.
This is growing widely popular in schools and colleges around England, as it gives you an excuse to start a rumor and get everyone talking. There has also been, in some cases - a "Tricking Tuesday"
Samantha: Im pregnant
John: but we used protection
Samantha: I know, i dunno how this happened.
**John gets all wound up the whole day**
- then the next day:
Samantha: Gosh, John! You are so gullible. I'm not really pregnant! Happy Tricking Thursday ;)