Being that the bracelets show support for Breast cancer awareness and research, I am sure most females would like the fact that even males are sporting them. Most women have been or know of someone who has been impacted by breast cancer and any and all support of this devastating disease should be looked upon favorably.
It depends on the girl and the reason the guy's wearing it. If the guy is a chauvinist and is showing off his sexual prowess, many girls would be offended. Other girls would find that sexy in a silly way.
If the guy is a halfway modest guy and is showing support for the awareness, many girls would find that very attractive. Others, however, would think he's still wrong for wearing something that says boobies. A third set of girls would not find it attractive because they don't want a guy who actually stands for something. This latter group is relatively small.