I got a 62 as my final grade in an easy core class
Is there a reason why you scored so low?
I went out and partied with friends when I should have been studying, and had too much booze and cigs.
It's important to try hard in school and to study for important tests, even easy ones, because your education will pay off in the future.  Bad grades and failed classes can prevent you from graduating, so take care of your classes first, and then celebrate at parties afterwards, when you can truly relax.
I got 12 other classes that are easy and I can pass anyways. It's not a big deal.
Well I'm glad that you are passing your classes, even if you aren't putting in much effort, and as you said, this was just an easy class.  However, the knowledge that you will gain from these classes could really pay off for you in the future, so give them more attention.  And besides, the classes will only get harder as you advance.