SUP – What’s Up
We use “what’s up” almost every day, but if it becomes shorter such as “sup”, it will easy to use when we send message or email. Meanwhile, when people say “what’s up” quickly, it will easy to become “s up”, so, “sup” is more convenience.
IDK – I Don’t Know
It is very common to use “IDK” to take the place of “I don’t know” when we sent message or email someone. However, people usually use “IDK” to someone who is much closed, otherwise, he/she will think that you are impolite.
WBU – What About You?
We usually use “what about you” to ask for the other person’s opinion, or to check for their comfort level with the situation. Because “a” in “about” pronunciation almost silent, so people say “wbu”.
I found some sentence from this website: