Underage drinking rules, especially in the dorms, are pretty strict. You won't get expelled over it but you will have to report to the dean and your parents will probably be notified. Plagiarism is a completely different story. I have had a few people in classes over the years who have been expelled for plagiarism. Attendance is usually lenient except in basic studies (some teachers allow only 2 absences); once you get into upper level courses they usually tell you you're an adult and can come to class when you'd like (i.e. you're accountable for yourself).