Sometimes, in college, you're going to miss a class or two. This oversight could be due to any number of factors -- too much jungle juice, a busted alarm clock, being stuck in some pesky prison cell -- but the important thing is coming up with a plausible excuse. Professors have heard it all before, so you'll need something rock-solid, completely believable and too humiliating to question.
Tell the professor (over email, if possible, though you might need to bite the bullet and go to office hours) that you woke up early, hit the dining hall and gym, then returned to the dorm to prepare for class. Your tone should be slightly incredulous. You're a busy, complex person juggling a full load of academic and extracurricular responsibilities.
Mention what kind of cereal you had at the dining hall, what was written on the butt of some girl's sweatpants. These are the details that will sell your story.
You returned to your dorm room sweaty and fired up for the day's lessons. You noticed your roommate was still asleep, snoring away. You put on your shower sandals and shuffled down the hallway to the bathroom. In the shower, you lathered up and recited Latin declensions or some other productive, class-related activity.
At the sink you brushed, gargled, flossed. When you returned to the room, however, the door was locked. You knocked, then pounded, calling your roommate's name with increasing volume as hallway traffic picked up. The drunk idiot was out cold; he just doesn't take his studies seriously. This mentality is lost on you. You vowed to call a room meeting THAT NIGHT. Dude eats all your trail mix and drinks all your soda.
The point is, you're locked out, in your bathrobe or pathetically wrapped in a towel. Your clothes and homework are in the room, inaccessible. It crosses your mind that your roommate might be dead. Maybe he choked on his own vomit. These things happen.
Class is about to start. You're still pounding. A neighbor comes out of his room, says he saw your roommate hustle out a few minutes prior. Your keys are inside. What now -- walk down to the front desk and get security to open the door? That's what you'll have to do. File some report. Just another indignity. Welcome to college.
So that's the excuse. You can pretty much copy-paste this into the email and change the pronouns. But be careful. Don't use this more than once per semester, or with more than one professor. They talk, and the odds that you were locked out naked twice in a matter of months right before a class begins are low. Then all the goodwill you've generated with this excuse goes right out the window. The professor will feel used, dumb. Professors don't like to feel dumb.
And if all else fails, just say you have mono.