Okay -
Done the sixth form thing myself. Had son go through the sixth form thing.
1. Don't wind the teacher(s) up. The only ones that lose out are you and any other classmates you disrupt. Even if you don't like the teacher, you've no right to spoil a lesson for others who may be enjoying the subject, be passionate about it, require a decent grade to go on to university. Disrupting lessons by winding-up the teacher is harming your peer's learning.
2. Arriving halfway through a lesson is not slightly late, it's hugely late and shows disrespect to not only the teacher but to any other students in the lesson.
3. You don't have to go to university. It's not for everyone and that's okay.
4. Even if you don't go to university, but go on to get a job, you are going to require a reference from your sixth form. If you've been acting like a spoilt brat, winding-up teachers and turning up late, why should they give you a decent reference? So you are harming your future chances by disrespecting teachers.
5. Keep your options open. Although you may not want to go to university now, you may change your mind in the future. This is entirely normal. It's entirely normal to not know what you want to do at this point in your life. But to keep your options open, you NEED to put more effort in now, and that means not worrying about university. That is not an excuse, however, to disrespect your teachers and your peers in lessons.
6. Think about the pros and cons of having a year out once you've got sixth form done & dusted. Whether it's to get a job or do a spot of travelling - whatever - that year out can be hugely beneficial for many who use it as a time to work out what they do want to do with their lives for the next few years at least.
7. Don't ruin your chances, whatever route you go (job, university, travel... whatever), by acting like a brat now.