1. Someone who doesn't know about or observe basic health or safety rules pertaining to various activities and/or doesn't speak up quickly enough when he realizes he is sick or injured, resulting in a painful and/or ruinous event for himself - which he then cathartically displaces onto someone or something else.
2. Someone who expects to overindulge in a lot of enjoyable or pleasurable or cathartic activities in rapid succession (all of which someone else pays for and/or has to clean up after) without allowing enough time to pass between them or without making enough effort to separate them. Due to his own negligence or unwillingness to wait/slow down when he should and his inability to move more quickly/speed up when he should, he creates unnecessarily huge messes that someone else has to deal with/clean up.
Basically: if you date a lot and start to notice a pattern in which you have two basically pleasurable and voluntarily-undertaken relationships in a row, which are always or frequently followed by a 3rd relationship that feels forced upon you and is rather intense, scary, embarrassing and disorienting - but ultimately you survive it and feel relieved afterward - you are possibly or probably a Mario.
Gastrointestinal example: You eat too much peanut butter because it is yummy. Immediately afterward, you do karate for an hour, which is fun. You then have a horrible case of diarrhea. You barely make it to a public bathroom, then spray it all over the bathroom because you can't make it to the toilet seat in time. You feel relieved, make no effort to clean it up and leave it for the maid to deal with. You never feel any guilt about it. You = Mario.