Penn has mentioned a few times on his podcast that him and Rob Pike are good friends from way back, and has shared several anecdotes.
One I remember and found funny was that one time Penn saw Rob talking to someone, and Rob asked for their phone number. From Penn’s vantage point he sees Rob pick a pen and paper and mimics writing the phone number, but doesn’t write anything at all. When he questions Rob about it he says something to the effect of “Oh, I can just memorize a phone number without a problem, but if I say that out loud they’ll think I’m blowing them off or I’m not really interested in the number, so it’s easier to just fake write it”.
One I remember and found funny was that one time Penn saw Rob talking to someone, and Rob asked for their phone number. From Penn’s vantage point he sees Rob pick a pen and paper and mimics writing the phone number, but doesn’t write anything at all. When he questions Rob about it he says something to the effect of “Oh, I can just memorize a phone number without a problem, but if I say that out loud they’ll think I’m blowing them off or I’m not really interested in the number, so it’s easier to just fake write it”.