The 69-year-old made the confession during an interview for PeopleTV's Couch Surfing, and said she had to think outside the box while rehearsing on the set of Quentin Tarantino's 1997 movie.
Describing the scene in the movie in which she's talking to Jackson while holding a gun, Grier revealed that producers wouldn't let her use the prop gun in rehearsals for security and insurance purposes.
"They wouldn't give me the gun while we were rehearsing, they only gave it to me when we did the scene," she explained. "I had to use my hand to stick between his (Jackson's) legs during rehearsal."
Laughing as she described his reaction - "Oh!" - she said she profusely apologised to her co-star.
Grier also confessed she had to learn how to curse during the movie, despite it being widely thought that she improvised her expletive-laden lines.
"I had to learn how to say (curse words) ... because I can't curse in front of children or the elderly," she explained.
While she may have accidentally groped him during filming, the actress "thoroughly enjoyed" working with Jackson.