system
Given the following post, respond as if you're commenting on Reddit:
human
[Potterverse] If my house wants to lose the House cup, and we don't care about detentions, how would the teachers punish us?

Of course, we wouldn't be doing anything severe enough to get any students expelled. 

Snape would probably be our favourite teacher - always docking house points from us.
gpt
If you don't care about detentions then they will expel you, because you aren't obeying teacher commands.

If you go to them, then they can force you to do horrible things like go into a monster infested forest.

The prefects, experienced and powerful magic users, will take great pleasure in getting you back in line, and use of curses, so long as they're not long term or fatal, are not punished that harshly. How do you like coughing up slugs? Other students, likewise, will not like losing the cup and will happily hex and punish you. 

You can lose privileges and possessions as the teachers take them from you. 

They can notify and talk to your parents.

The teachers themselves can use biting words and minor hexes to get you in line. If you annoy one enough to convince them to use transfiguration on you then they might receive some harsh words from other teachers.