Are you kidding me?
I paid $130 for my last pair of jeans.
|RYFS||Are you freakin' serious?|
|LBS||Laughing but serious|
|BST||But seriously though|
|IDS||I'm dead serious|
|IDK||I don't know|
AYKM (are you kidding me) is an expression of shock and/or frustration. It is similar to AYS and RUS, which mean "are you serious," but meant to convey just a bit more exasperation.
For example, if you borrow your friend's car, crash it, and then text them to say so, they might respond with AYKM. This indicates that your friend a) can't believe you crashed their car and b) does not care whether you're okay.