Could brain tumors cause weird sexual behavior?

Brain tumors could: Cause all kinds of strange behaviors. It depends upon where in the brain the tumor is growing. If it is near the part of the brain that impacts on sexuality, it could occur. If you are concerned that you or someone you know has a brain tumor, consult with a physician.

Yes: Brain tumors can cause many disturbances of behavior including a form of hypersexuality called the "kluver-bucy syndrome". Patients with this syndrome may seek sexual contact with both men and women, and tend to use their mouths to evaluate any new thing in their environment. Usually these patients have disease, whether infection or tumor, in both temporal lobes.

Yes, most definitely, however keep in mind that neoplasm or tumor is not the only potential cause for aberrant sexual behavior. It can be seen in neurodegenerative disorders (Pick's Disease now known as frontotemporal dementia-example), manic states, schizophrenia or with CNS infections just to name some other possible causes. Kluver Bucy, well explained here, also has a number of possible causes