A preemptive flush occurs when one is sitting on the shitter, hears footsteps and flushes even if it isn't neccessary in order to let the person whose footsteps you heard know it's occupied, to deter them from coming into the toilet while you're doing your business.
A: I was sitting on the toilet mid-shit when I heard my sister's footsteps, I did a preemptive flush so she wouldn't come in while I was doing a blumpkin.
by Some_Random_Asshat March 31, 2018