Roughly it can be described as throwing one's hands up straight in the air and waving them left and right with the palms turned forwards. While doing this one swings his body left and right to create a snakelike motion continued by the lifted arms. The best overall impression is achieved by tensing one's lips to look like one is about to kiss.
Warning! The Mario requires a certain amount of flexibility and gayness of the spirit to be taken seriously.
"Hey that guy is doing the Mario!"
"That's no way to do the Mario!"
A girl gives you head and while she's down there you cum on her upper lip then when she looks up you pull out some pubic hairs and "Glue" them to her upper lip giving her a mustache, or a Mario