Allowing your front passenger to put thier feet up on the dash can cause serious injury.
Although it might be comfortable or your girlfriend has hot legs don’t let your front passenger put their feet up on the dash while driving. A typical passenger airbag deploys at around 330km/h with a force of 400kg.
Also a condition known as sub-marining may occur in vehicles with or without front airbags. Basically you slide under the seatbelt & into the dash & footwell area. A minor injury could become amputated legs.