Confidence

"Uh yea I can do that, I'm the best at that thing"

Once per long rest, when prompted for a skill check, flip a coin. On a success you gain expertise in prompted skill and gain advantage for that roll. On a successful roll you gain this expertise until this feat is used again. On a failed coin flip nothing changes. On a failed roll you loose the expertise.

You have disadvantage detecting if others are lying about their proficiencies.