Place it at the end of a short sequence, after a failed attempt clip has played out. Open with the I'm Batman soundboard button for a straight-faced DC setup, then let this clip close the bit as the reply that refuses to back down.
About this sound
This is a 1.8-second voice clip of Harley Quinn delivering the line about not knowing when to quit, in her bold, teasing delivery. It feels defiant and mischievous, like a proud admission of stubbornness rather than an apology. The short punch makes it land as a comeback for anyone who keeps going.