1. a person being notoriously good at something, but is the underdog of it; an urban myth of a rookie that shows up at the last second and slowly assasinates other competitors
2. a person who is a cerebral assasin
As in Skateboarding a McDiesel skater is Torey Pudwill
As in basketball a McDiesel player would be Mike Bibby
In Modern Warfare 2 a McDiesel would be a sniper in a distance that only gets headshots
Someone who is amazing at a sport or activity.
That guy is such a Mcdiesel at soccer.