- "You remind me of your father when he went here; he was a slacker too."
- —Mr. Strickland to Marty McFly
A slacker was a person deemed to have poor discipline. Mr. Strickland called many students that did not respect his level of authority "slackers", including Biff Tannen. To Strickland, most members of the McFly family were slackers.
When Strickland's house was terrorized in 1985A, he confronted Marty McFly (who he had never seen in this version of reality) with a shotgun and said "I've never seen you before in my life, but you look like a slacker." Strickland was about to shoot Marty — or, judging from where he was pointing the weapon, literally destroy Marty's prospects of fathering children by Jennifer Parker forever — when his house came under attack by one of the armed teenage gangs terrorizing the neighborhood, thus diverting his attention. Marty took the opportunity to escape as Strickland screamed "Eat lead, slackers!" before firing off the weapon in their direction. This is erased after burn the almanach in 1955.
When Marty introduced himself to Edna Strickland, she first identified him as "that McFly slacker".