This is where you get either male or female jizz on both your thumbs or two fingers and as quickly as you can draw a moustache starting from the middle of the upper lip and going outwards ...
KEY POINT : as you do this you MUST shout MARIO (In his accent is funnier) !
Sarah : 'Does that guy know he has a white moustache?'
Emily: 'Yeh looks crusty doesn't it?! '
Rachel : 'Yup I fucking MARIO'D him ;D '
Emily: GO MARIO !
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