As a Bipolar I, here are a few of my own myths:
1) If he's happy, he must be manic.
2) If he's happy he must be off his meds.
3) Sex is better when manic.
4) Bipolar's can't handle stressful jobs.
5) Drinking works as well as medication.
6) Depression and mania will go away with time.
7) Hallucinogens are safer on lithium.
8) I could never be so depressed that I would commit suicide.
9) Hypomania is safe and controllable.
10) All Bipolars are exceptionally intelligent. (OK, so that one is true)