Depending on the manner in which you do it…
If you subtly let them know you have a strong prejudice, they’ll tend to not have you on that jury.
If you blatantly tell them you’re not willing to be a fair juror, you may get sternly warned and/or fined and/or thrown in jail for a while for contempt of court.
Getting out of unpleasant jury is something they all know many people try to do. You’re in a competition with the other unwilling jurors too. Judges are smart and have developed their countermeasures. They tend to not put up with disrespect, and are good at spotting character, lies and deceit… and some may also be paranoid and defensive about it.
Being respectful and honestly open about your biases while not omitting that you know there is a legal obligation to serve as an unbiased juror to the best of your ability, seems like a good approach to me. Sometimes just displaying intelligence and free thinking, or unpredictability, may be enough for the lawyers to take you off, because they want to feel they can predict how each juror will decide.