Yes, men can have a concave profile to their nose. In general, a straight or convex profile is associated with a male face, while a concave profile is associated with female characteristics. This is not a rule, and exceptions for both genders abound (Barbara Streisand and a younger Kevin Bacon are good examples). The shape just changes the overall nature of the face. The best way to see this is with computer imaging (or just try using Photoshop at home, and play with the variations!). It really boils down to personal preference, which is why a surgeon should never tell you what nose you should have. It is your nose you have to see every day, and you should be happy with it.