Students sit in groups of 3 to 5. They should play janken to decide the order of students (or however way they want to decide).
Show a slide, and they must choose if A or B, both A and B, or neither A or B, is okay by common school dress code rules. The student who's turn it is to play will stand up and raise their hand for A, B, C, or D. If they get it right, they get a point. (I usually have the students close their eyes so they can't just copy what other groups are doing). The system I use is as follows:
A: A 〇 B ✖
B: A ✖ B 〇
C: A 〇 B 〇
D: A ✖ B ✖
The explanation of each rule is in the speaker notes. Be sure to mention that there are no national rules and that every school is different. These are simply some common ones.
After the first set of questions, the powerpoint shows two people, one compliant with dress code and one not. They must choose which one is correct, and can get a bonus point if they raise their hand and explain the reason.
The high school kids I taught got surprisingly into this and it felt much better than just giving a presentation about dress code (which is what my JTEs originally asked me to do), but I'm sure it would also work well with JHS. Kids thought it was fun to learn about all our different, sometimes strangely specific, rules.