Bucking the mustard
Bucking the mustard is basically having diarrhea so bad it's squirting yellow from your rectum like someone's squeezing a bottle of mustard and it farts towards the end. Generally followed by the sound of someone scrubbing the shit splatters off the side of the bowl.
Man, I was up all night bucking the mustard.
Jill: Yeah don't bother coming to work, I don't want what you have.
man: I will call tomorrow and let you know if I am feeling better.
Jill: Okay
Jill: Yeah don't bother coming to work, I don't want what you have.
man: I will call tomorrow and let you know if I am feeling better.
Jill: Okay