When an upper-classman dates a younger female at a school. "Clarkers" will usually have a string of failed relationships that only lasted for a few weeks. Those who clark usually do so because they are infamous around school and no girls in their grade want to date them, it is because of this the clarker usually takes advantage of the newer girl's ignorance pertaining to who the clarker really is.
The bigger the age difference between the clarker and the victim, the more pathetic it becomes (ie a junior dating a freshman is worse than a sophmore dating a freshman)
Someone is not clarking if they have been dating the younger girl for more than 6 months, or if they have only clarked once.
Person 1: "Dude Josh was picking his nose in class again."
Person 2: "The guy who shit himself in math last year?"
Person 1: "Yeah! I heard he has another freshman girlfriend this year."
Person 2: "Probably because she doesn't know how gross he is."
Person 1: "Poor girl doesn't even realize she's a victim of clarking."
Person 2: "Wait wasn't he with Taleene last week?"