You know, I wanna thank WWE. I haven't marked out like this in 8 years.
WTF does Marked out mean?
Basically, to go crazy happy at whatever just happened. Derived from the term 'mark', meaning someone who fully buys into the story (Oftentimes to the plot of believing it's all real). "Mark out" is a term for something that hardcore smart marks (Or 'smarks', guys who know about the backstage business) go crazy happy over.
For example, I follow the business pretty closely, so I don't really go wild for something like John Cena's Attitude Adjustment like most kids in the audience will. However, I got that same level of happiness when Daniel Bryan, my favorite active wrestler in the world today, won his Money in the Bank match, and is now all but guaranteed to hold a major world championship within the next year. Thus, I marked out for that moment.