Meh, if you had a good excuse it probably wouldn't look bad. But if your excuse is, "Oops, I hadn't realized I already had all my math requirements. So, I decided to do a pass/fail. That way, I wouldn't have to work for a class I didn't need." Well, that isn't a good excuse. It makes you look like you didn't plan your schedule well AND would rather take the easy way out than buckle down and get the A. If it isn't going to give you a C, I'd advise that you keep it listed as a graded class.