Most recently (early last year) I've sat in an AirFrance a320. All pax already boarded, but then flight had to be put "on hold" cos of bad weather in CDG. On a whim I asked the FA whether I could visit the cockpit since we were grounded anyway, captain said yes, so I sat in the jump seat in the cockpit chatting with both pilots for a good 15mins before getting kicked out for the flight to depart.