You're a freshman. And every new environment takes some getting used to. But really: exposed nipples have no place in the classroom.
I don't care that you're male. And I don't care how badass slashing up your lacrosse t-shirt makes you. And while I might in other circumstances celebrate the comfort with your body suggested by those bits of fabric flopping across your flesh, in Composition I prefer not to.
And don't pick at those blemishes. It only makes them worse.