The tilde (~) is used several ways.
1. It can be use in chat to make a word seem longer, such as in example 1.
2. It can also be used in chat to clarify sarcasm, as in example 2.
3. This key is very commonly the "console" key in most flash games that are editable.
1. This lecture is so~ long (instead of sooooooooo long)
2. I'm so sure~ -or- I bet it is~
3. Any flash games.