When a girl is teasing a boy by mouthing "Olive Juice" to him, but with the perception she is mouthing "I Love You." Boy develops crush on girl, only to be found out later she actually had a crush on him as well. Slang.
"Teresa mouthed 'Olive Juice' to Tammy from across the room. Mike was in the middle and had a crush on Teresa. He thought she meant 'I Love You.' Years of confusion ensue."