This is plain and simple, when your getting sexual with someone and then once the man cums (it can be with female juices too ;D ) get some jizz and quickly draw a moustache starting inwards and going outwards and shout 'Its'a me MARIO!!'
Sarah : 'What is white stuff on that girl/guys moustache?'
Emily: 'LOL its crusty!'
Rachel: 'Yes I fucking mario'd him ;) '
Hence mario moustache