When a fart is conducted in the shower and the water running over the anus makes it sound like a duck quacking.
Friend 1: "I farted in the shower earlier and it sounded like Donald Duck laughing."
Friend 2: "SHOWER QUACK!"
The act of farting in the shower as water muffles the noise causing it to sound somewhat like Donald Duck laughing.
I took a shower earlier and farted, sounded like Donald duck laughing, a total Shower Quack