Yes, you can put these in the ''know them but never use them'' category. You'd never really use these, unless you want to sound illiterate.

These are not really abbreviations. They are street slang and only good for talking with your friends . But still bad English. please don't use these in an email or letter. In a rap song would be ok

1. Why is 2. Because 3. Don't know (Do not know)