One day you're attracted to guys, and girls disgust you. The next you're attracted to girls, and guys disgust you. The day after you're attracted to squirrels, and humans disgust you, etc.
Omnisexual people often exhibit signs of sexual bipolar disorder.
Burt: "Woah hold on man, Josh is sick. He's suffering from sexual bipolar disorder"
Jim: "Oh, wow. I'm sorry that I insulted him, that sounds tough."
*Josh having sex with a tree in the background*