Throughout the Back to the Future series, we see that Strickland, sorry, Mr Strickland calls Marty a 'slacker' and George a slacker, even the guys shooting at his house are slackers. Do we know of anyone who Mr Strickland doesn't think as being a slacker? Non-canon answers will be accepted. I would be especially interested to see whether this is mentioned at all in the television series.
The only person I can recall whom Strickland mentions, but doesn't call a slacker, is Doc Brown. Strickland labels Doc a "dangerous... nutcase", but not a slacker.
Let me give you a nickel's worth of free advice, young man. This so-called Dr. Brown is dangerous. He's a real nutcase.
But the Back to the Future wiki seems to suggest that the actual number of people deemed by Strickland to be "slackers" is relatively small: