(1) For a male to gladly remain in the friendzone with a female while still fantasizing about sex with them.
For a man to be truly "marklar'd", he must be designated as "one of the girls". A shoulder to cry on, someone for girls to ask insight about their male companions thought patterns, etc.
The most important part of being marklar'd however is never even attempting sexual relations. You must remain completely platonic, even though the thought of sex has never left your mind.
(2) Posting pictures of your buddies girlfriends and other friend-zones on the internet message boards and referring to them by pet names and speaking of them sexually.
(1) Dude, that girl at the bar was all over you. But after you insisted on talking to her about manga for 30 minutes, you got marklar'd.
(2) Yo!! dude marklar'd your chick on this forum!!