Verb. The act of taking a drink of some foul-tasting, usually very high-proof liquor without making any facial expressions that would indicate that it does in fact taste horrible. This is a reference to the fact the Mark Wahlberg often says extremely stupid shit with a very serious face.
Me- "Damn did you see that guy just marky-mark that shot of 151?!"
Brent- "That's one stern motherfucker."