Just to offer an alternative theory to the other answers:
What you should do is almost entirely contingent on your company culture and the practices established by your companies HR for hiring. I do know of software companies where teams are considered sacred (if you will) and the team has the final say on all hiring and firing. Granted, the teams are generally well established, well organized and require very little supervision. That's why they are allowed that responsibility and can basically override their boss on team building decisions.
If your workplace functions in that way, and if your team is a well established team, then you might consider having an informal (off the record) chat with HR regarding the situation. If there are established guidelines for hiring that say "the team will have a say in who is hired and who is fired" then you may have some grounds for filing a formal objection.
But, be very careful doing this, I can't imagine your boss will take it very well. Even if the objection were successful, and you were allowed to hire this person, the working environment could become pretty nasty if your boss and one of your co-workers despise each other. And you won't look so great either (in your bosses eyes) for forcing the issue and bringing them on to your team.
If, though, your company culture is that the boss is the boss and has the final say in all hiring and firing, then you are simply at an impasse. You could protest, certainly, but I'd only recommend protesting if you really feel that this is something worth losing your job over or, at very least, forever altering how your boss views you for the worse. If you have other job options though, and feel you could leave this job easily, and you feel very very strongly about this then, well, perhaps you could speak up.
Just understand, you may be putting your job, as well as the jobs of your co-workers, on the line by doing something like that. At that point you must ask yourself, "is it really worth all of that risk to try and force this person that my boss dislikes onto the team."