Isn't that what spacebar does? A roll based on charisma?
At least it seems to be random who wins the argument.
If you'd reload anyway, just use the keyboard to switch to the next party member and back during RPS and you'll auto-win the argument with NPCs (don't use this in player-player dialogue though, the conversation will be stuck in a loop)
Spacebar seems random. Using it I've won battles where the opponent had +6 points to my +3. So it definitely doesn't go to the one with the most charisma.
