Was Marty considered a bad kid?

Was Marty a bad kid? Depends on your perspective.

Marty was probably in "trouble" a lot at school for being distracted, being in the wrong place at the wrong time, or for opening his yap when he should have kept quiet.

That doesn't make him a bad kid to me but might to someone uptight like the principal or the father of a teenage girl who would fine *any* young man a "bad" kid.

I don't think he was a "bad" kid, per se. He just wasn't popular and was more of an outlier and a rebel that people chose to treat like crap. I think he was also a target for bullying, though unlike his dad, Marty was strong enough to stand up for himself and fight back, which probably led him to getting in trouble and sent to the principal's office a lot (I know, I was in a situation similar to that while growing up).

Remember that the parents and grandparents in that town were from an era (mid-20th century) where reputation meant everything. Plus, it was a small town, so everyone knew everyone. Any reputation the parents had was reflected on the kids, regardless of how different the kids tried to be. So since most people in the town knew Mr. McFly to be a wimpy loser, they would just assume his son was a loser too, despite Marty's efforts to be better or different.

Word is he is a slacker, from a family of slackers.

He may have a reputation as a bad kid from some people, but we as an audience know he isn't a bad kid. Though I did always notice little things like his girlfriend's dad looking annoyed with him, as you pointed out.

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I never took Jennifer's dad's reaction to be against Marty, per se. More that he was just trying to hurry Jennifer along. They were going to visit their grandparents after all.

But to answer your question, the only other interaction we see Marty having with adults of his own time (who weren't The Doc), was with his parents and Strickland. His parents don't tell you much, because pre-time travel they both came across as pretty useless as parents, and Marty was just sat there silently the whole time they were eating together.

Strickland, though you could argue treated every kid like they were awful, at least told us a few things about Marty. We hear that he's been late to school four times in a row. Also, that he considers The Doc to be dangerous and a bad influence on Marty. Also, we see Marty sarcastically rebuke Strickland's advice.

So, I'd say Marty was considered far from the perfect student, and somewhat anti-authoritative. But at the same time, Strickland was obviously a gigantic jerk, with a tendency to bully students rather than help or educate. So the audience are meant to sympathise with Marty in this instance.

I suppose in the next two sequels, when Marty overreacted to being called a chicken, and was easily lead into making stupid decisions, you could argue that's a character flaw.

I think really, we're supposed to assume he's a fairly normal teenager. Not angelic, but certainly not a terrible person.

I more see it that Principal Strickland is too much of a judgmental jerk and that the judges of the contest were anti rock jerks.