Referring to the situation when you have been up all night on your computer having pointless conversations with friends just to keep eachother awake. and then your mom goes all stealth mode and listens to your convo (sometimes from the ceiling wielding bazookas) or just a cup on the door. so you non-cholontly get up and walk to the bathroom and take a "chill flush". the action of chilling in the washroom not actually peeing but then flushing the toilet to make it believable. Then followed by the awkward meeting up with your not so stealth mom in the hallway and slyly asking(with a hint of disgust) why she would be awake at such a time. Thus, covering your ass for being up so late. and turning the late night encounter onto her.
"How did you flush it?"
"Just like pretty chill"
"like a chill flush, nothing crazy, just chill"