Bi stands for bismuth according to the periodic table of elements. You'll be sexually aroused with Pepto Bismol after trying it because bismuth contains toxic that you'll be tripping with.
Mack: Yo wants some ecstasy to get some sexy ladies?
Jim: Nah I'm Bi-Sexual. Pepto Bismol FTW!
Ryan: I'm sorry, Big Mac! I'm gonna be Bi-Sexual! You won't upset my stomach anymore, Big Mac!