You are more likely to be assumed promiscuous or slutty if you are bisexual.
I think @holden‘s perception about prejudices in our society is correct. I think that people who are considering getting involved with someone who is bisexual are sometimes (maybe even often) afraid that their partner requires a significant other of both sexes. They may also fear their partner will leave them for someone of another gender, so they have to be jealous of everyone, not just one gender.
We’ve had several questions here from people who are worried about getting involved with someone who is bisexual. Another concern may be that the person really isn’t bisexual, but is gay or straight, and eventually they will be dissatisfied sexually, and use that as an excuse to leave the relationship.
When people use labels to form an opinion about someone else, instead of using actual experience with that person, they tend to have more prejudices, it seems to me. Is “bisexual” a more fearsome label than “gay” or “straight” are? It could be. It might not be. I don’t think we can know unless we do a survey.
All right, I ran the numbers from the General Social Survey. I looked at the responses of gays, bis and hets for four questions I am putting in the percentages for “yes” answers:
1) IN LIFE, R HAS EVER BEEN HARRASSED ON JOB CUZ R WAS BELIEVED TO BE GAY/LES/BI
Yes: Gay: 41.3 Bi: 22.5 Het: 22.1
2) IN LAST 5 YRS, R HAS EVER BEEN HARRASSED ON JOB CUZ R WAS BELIEVED TO BE GAY/LES/BI
Yes: Gay: 72.6 Bi: 75.0 Het: 0.0
3) IN LIFE, R HAS EVER BEEN PREVENTED FROM MOVING CUZ LANDLORD BELIVED R WAS GAY/LES/BI
Yes: Gay: 5.2 Bi: 2.2 Het: 0
4) IN LIFE, R HAS EVER BEEN DENIED A JOB OR FIRED CUZ EMPLOYERS BELIEVED R WAS GAY/LES/BI
Yes: Gay: 26.6 Bi: 4.3 Het: 1.5
So on three questions, gays believed they were discriminated against more than bisexuals. On only one question (have you been harassed on the job in the last five years because you were believed to be gay or bisexual) did bisexuals say they experience more discrimination than gays. The answer to this question is belied by the similar question (have you been harassed on the job in all your life because you were believed to be gay or bisexual).
So, in conclusion, I’d say that you are less likely to be persecuted if you are bisexual than if you are gay.