We call it a suburban critical after someone took (humorous) offense to the term ghetto critical.
Since nobody else has responded in two days, I was going to make a prurient reference to tap-and-die; but I had an attack of conscience, so I'll limit myself to this: My guess is that they lightly tap one finger on top of the d20 to demonstrate that they do know where their d20 is located, but aren't even going to bother to pick it up, much less to roll it."Tap the Die" This one I've been told comes from the southern states (FL to be exact) during RPGA games. It means the PC knows the DC of the skill already and doesn't even need to roll it to make it ( ie Tumble checks or Concentration checks).
Why "tap"?
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(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.