Law students always seem to have this bizarre competitive streak to the point where if you did well in a particular subject they'll badger you for your "secret techniques". There are always secret techniques, because clearly you didn't get that mark through luck or just learning the coursework... you got it by ignoring certain areas, doing extra research in these journals, finding these books, getting this person's summary etc....
I don't hate that, to be honest... seeing that attitude in first years is actually cute in a, "you're becoming a true law student, how funny" kind of way.
Anyway, my pet peeves are:
1) Laptops in class. I shouldn't care, but I do. I hate the constant white noise of typing that occurs in law lectures. Learn to use a pen guys, you don't need to take down the lecturer's every word.
2) People who've clerked and consequently know everything about the law. The same goes for people who think that they're James fucking Bond because they worked in a Government Department and had to get cleared by security to get the job.
3) Loudmouths in assessable tutorials who think that they need to shout everyone else down to ensure that they get the maximum mark. The kind who ask questions when they know the answer, turn questions into statements just to say something or lecture the lecturer.