It won't look especially bad. Like alethiometer said, a pattern of withdrawals will look bad, but a single withdrawal or even a few withdrawals with a good reason ("I broke my leg over Christmas break and until January I didn't realize how many of the elevators on my campus are completely unreliable" is a whole lot different from "Eventually I realized that going to class was completely incompatible with my rum-soaked lifestyle") isn't too bad.
However, if it's something you've got to take or if it's a class of a type you've got to take, you're going to want to prepare to do better the next time around. And if it's in a class in your major or in a subject that the faculty at your grad school take seriously, that's especially true.
If it's a class your major requires, then depending on your definition of "kill" (there are people who can't bear to see their transcripts marred by a B and people who can't bear to see their transcripts marred by a D, and that's two totally different things) and the likelihood that you'll do better on a second attempt, it might be better to make a less-than-ideal grade in your freshman year and then move on to do better in subsequent years.
Everybody makes mistakes, but what you're shooting for is to learn from them the first time you make them and to make fewer as your academic career progresses.