You need much larger variable latency range to be truly annoying. I'm talking high enough that someone backspacing over a mistake will think that the interface

You need much larger variable latency range to be truly annoying. I'm talking high enough that someone backspacing over a mistake will think that the interface didn't receive the input. So they do another backspace. To get it just right you'd probably trigger the initial backspace callback immediately after the user types a 2nd backspace. Then wait a long time before triggering the 2nd backspace callback. Since the original problem character has been removed the user will most likely try to continue typing. Finally, update the queue of characters all at once-- starting with the 2nd backspace. Now the latency has caused a character right before the queue to get eaten. This is how you cause people to throw their device against a wall.