1) Cocaine is a hell of a drug
2) He is grieving, anger is a pretty common response. Especially for someone who isn't introspective like Craig. Someone like him is less likely to get hung up on the depression and sadness but anger can be harder to let go of because you have to recognize it.
I also think both Craig and Darren are taking out their anger on Jay. Smurf basically used her will to call them fuck ups but since she isn't there to be mad at Jay is a convenient target.