By day, John C. Layfield is an investment banker and professional pontificator for Fox Business Network. By night, he peddles a love potion.Mamajuana Energy, a berry-flavored liquid that Mr. Layfield developed, sells for $4.99 or less. He bills the two-ounce shots as an all-natural “sexual endurance drink” for men. A minister’s son, Mr. Layfield says he first sampled the concoction in a dive bar in the Dominican Republic while on vacation and was hooked.“It’s more of a sex potion,” said Mr.…See More